Chapter-9: AWS Solution Architect Past Interview Questions-Part-1.
Question: What is RTO and RPO?
Answer: RTO (Recovery Time Objective) is the targeted duration of time and a service level within which a business process must be restored after a disaster in order to avoid unacceptable consequences associated with a break in continuity.
It determines how long you can afford to be without your data before the business suffers. RPO (Recovery Point Objective) is the maximum acceptable amount of data loss measured in time. It defines how old the data might be when the system is recovered. Essentially, it represents how much data a business can afford to lose.
Question: What is ARP?
Answer: ARP (Address Resolution Protocol) is a protocol used in the IP network layer for mapping an IP address to a physical machine address that is recognized in the local network. It is crucial for IP operations as it facilitates the communication between Ethernet and IP addresses on a local area network.
Question: Design a 3-tier web application, where it should be able to support 1 million users simultaneously. Also, you have to make sure that the website is highly available? You will be asked various questions based on this design.
Answer: A 3-tier web application typically consists of the presentation layer, application layer, and data layer.
- Presentation Layer: This is where the end users interact. Use a global Content Delivery Network (CDN) to serve static content, ensuring faster load times and reducing load on the main servers. Employ a load balancer (e.g., AWS ELB) to distribute incoming traffic among multiple application servers.
- Application Layer: Deploy the application on multiple servers across different availability zones or even regions. Use auto-scaling to handle spikes in traffic. Statelessness is important to ensure any server can handle any request. For session management, use a distributed cache or a service like Redis or Memcached.
- Data Layer: Use a distributed database system that can handle a high number of IOPS and has replication across multiple zones/regions for high availability. Consider databases like Cassandra, Amazon DynamoDB, or even sharded relational databases. Regularly backup data and have a failover mechanism in place.
Ensure that the entire infrastructure is monitored with adequate logging and alerting mechanisms. Implement health checks to ensure high availability. Data security and regular vulnerability assessments are also crucial.
Question: What is OSI Model and describe each layer in it?
Answer: The OSI (Open Systems Interconnection) Model is a conceptual framework used to understand how different networking protocols interact across networks. The model consists of seven layers:
- Physical Layer: Deals with the physical connection between devices. It defines the hardware elements involved, such as cables, switches, and NICs.
- Data Link Layer: Responsible for creating a reliable link between two directly connected nodes. It provides addressing via MAC addresses and error correction.
- Network Layer: Determines the best path to route data from the source to the destination using logical addressing (like IP addresses).
- Transport Layer: Ensures reliable data transfer between two devices on a network. It uses ports to distinguish different services and can break data into chunks or segments for transmission.
- Session Layer: Establishes, maintains, and terminates connections (sessions) between applications on different devices.
- Presentation Layer: Transforms data from one presentation format to another. It deals with data compression, encryption, and translation services.
- Application Layer: The interface between the networking stack and end-user applications. It provides network services to applications and user processes.
Question: What is the LAMP stack?
Answer: The LAMP stack is an acronym for a popular set of open-source software used to get web servers up and running. The components of the LAMP stack are:
- Linux: The operating system.
- Apache: The web server software.
- MySQL: The relational database management system.
- PHP: The programming language used for web development (though it can also stand for Perl or Python).
Together, they provide a proven set of software for delivering high-performance web applications.
Question: What is WAF and how it differs from the Firewall?
Answer: WAF (Web Application Firewall) is a specific type of firewall that monitors, filters, and blocks HTTP traffic to and from web applications. It specifically focuses on protecting web applications by inspecting HTTP/HTTPS traffic to prevent web application attacks, such as SQL injection, cross-site scripting (XSS), and more. A traditional firewall, on the other hand, focuses on controlling network traffic based on IP addresses, ports, and protocols. In essence, while both provide security, WAF protects at the application layer (Layer 7 of OSI Model), and traditional firewalls operate mainly at the network layer.
Question: What is the difference between container and virtual machine, what is better in which situation?
Answer: A container is a lightweight, stand-alone executable package that includes everything needed to run a piece of software, including the code, runtime, system tools, and libraries. Containers virtualize the OS, sharing the same OS kernel, while isolating the application processes from each other. Docker is a popular containerization platform.
Virtual Machines (VMs) virtualize the entire hardware to run multiple instances of full-fledged OS. Each VM includes both a full copy of an OS, a virtual copy of all the hardware that the OS needs to run, and an application.
Question: When to use Containers?
Answer:
- When you need faster start-up times.
- When you want more efficient utilization of underlying resources.
- For microservice architectures.
- When you need consistency across multiple environments.
Question: When to use VMs?
Answer:
- When running applications that require all the resources and functionality of an entire OS.
- When you need to run multiple applications on servers with different OS requirements.
- When a higher degree of isolation is required.
Question: What is the difference between cluster and mirroring?
Answer: In the context of databases:
- Cluster: A cluster consists of two or more servers that work together to provide high availability, load balancing, and failover capabilities. Clustering distributes the workload among all servers, maximizing throughput and capacity. If one server fails, the workload is rerouted to the remaining servers.
- Mirroring: Mirroring is a solution to provide a high-availability data protection by creating an exact replica of a database on another server. If the primary database becomes unavailable, the system can switch to the mirrored database, ensuring continuity of operations. Mirroring typically involves two servers only: a principal server and a mirrored server.
Question: What is the SQL and NoSQL database, can you give me the example in which situation you would prefer NoSQL over SQL?
Answer:
- SQL (Relational Databases): These are traditional databases that use structured query language (SQL) for defining and manipulating data. Data is stored in rows and columns in tables. Examples include MySQL, PostgreSQL, and Microsoft SQL Server.
- NoSQL: Refers to non-relational databases that do not use SQL as their primary query language. Data can be stored in various ways: key-value pairs, wide-column stores, document stores, or graph databases. Examples include MongoDB (document store), Cassandra (wide-column store), and Redis (key-value store).
Question: When to prefer NoSQL over SQL?
Answer:
- Handling large volumes of data with diverse structures.
- Need for flexible schema or schema-less data model.
- Quick and iterative development cycles.
- High-speed, scalable, and distributed systems, like real-time analytics.
- When dealing with hierarchical or multi-valued data, as in the case of JSON-like documents.
Question: What is horizontal scaling and vertical scaling?
Answer:
- Horizontal Scaling (Scale Out): This involves adding more servers to the existing pool or cluster to distribute the load, essentially scaling out by increasing the number of nodes in the system. This type of scaling offers high availability as there's no single point of failure.
- Vertical Scaling (Scale Up): Involves adding more resources (CPU, RAM, storage) to an existing server. It's about making a single node in the system more powerful. However, there's a limit to how much you can scale up due to hardware constraints and potential single points of failure.
Question: What is monolithic architecture?
Answer: Monolithic architecture refers to a software design where all the components of the application (like user interface, data access code, and business logic) are bundled together tightly into a single codebase and run as a single service. Changes or updates to any component often require building and deploying the entire application anew. Monolithic applications are typically easier to develop and test initially, but they can become complex and hard to manage as they grow.
Question: What is microservice based architecture and how it is different from the monolithic architecture?
Answer: Microservice architecture is a design approach where an application is broken down into a collection of loosely coupled, independently deployable services. Each microservice usually corresponds to a single business capability and communicates with others over a network, often using HTTP/REST or message queues. The key differences from monolithic architecture are:
- Modularity: Microservices are modular and independent, while monoliths are typically a single, tightly-integrated unit.
- Scalability: Each microservice can be scaled independently based on demand, whereas in monolithic architectures, the entire application must be scaled.
- Deployment: Changes in one microservice can be deployed independently without affecting others, whereas changes in a monolithic application typically require the whole application to be rebuilt and redeployed.
- Technology Stack: Different microservices can use different technologies, libraries, and databases, but monolithic applications typically have a single unified technology stack.
Question: What is Data Warehouse and how it differs from Database?
Answer: A Data Warehouse is a large, centralized repository of data that is specifically designed for query and analysis. It aggregates data from multiple sources, making it easier for businesses to derive insights. Differences from a standard operational database include:
- Purpose: Databases are designed for regular transactional operations (OLTP - Online Transaction Processing), while data warehouses are designed for analytical processing (OLAP - Online Analytical Processing).
- Design: Data warehouses often use denormalized data structures to optimize query performance, whereas operational databases often use normalized structures to optimize update/insert performance and minimize data redundancy.
- Size: Data warehouses usually store a larger amount of historical data compared to databases.
- Integration: Data warehouses typically pull data from various sources and provide a unified view.
Question: What do you mean by hypervisor?
Answer: A hypervisor, also known as a virtual machine monitor (VMM), is software, firmware, or hardware that creates and runs virtual machines (VMs). It allows multiple operating systems to share a single hardware host. There are two main types of hypervisors:
- Type 1 (Bare Metal): Runs directly on the host's hardware to control the hardware and manage guest operating systems. Examples include VMware vSphere/ESXi, Microsoft Hyper-V, and Xen.
- Type 2 (Hosted): Runs on a conventional operating system (the host OS) as a software layer. Examples include VMware Workstation and Oracle VirtualBox.
Question: Explain the usage of OSI Layer-4 and OSI Layer-7?
Answer:
- OSI Layer-4 (Transport Layer): This layer ensures the reliable transmission of data segments between points on a network, including segmentation, acknowledgment, and error recovery. Protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) operate at this layer. It's also responsible for end-to-end flow control and establishes, maintains, and terminates connections.
- OSI Layer-7 (Application Layer): This is the top layer of the OSI Model and directly interacts with end-user applications. It provides network services to application processes. Common protocols at this layer include HTTP, FTP, SMTP, and more. It's responsible for data formatting, encryption, and compression, and also ensures that the sender and receiver are communicating in a compatible format.
Question: Can you explain the Load Balancer working?
Answer: A Load Balancer is a device or service that distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed with too much traffic. This helps maximize responsiveness and availability. The working of a load balancer includes:
- Traffic Distribution: Based on algorithms like round robin, least connections, or response time, it distributes client requests across multiple servers.
- Health Checks: Periodically checks the health of servers. If a server is found to be down or not responding, it stops sending traffic to that server until it's healthy again.
- SSL Termination: Handles the SSL handshake and decrypts incoming requests and encrypts responses, offloading the SSL overhead from the actual servers.
- Session Persistence: Ensures a client consistently connects to the same backend server, essential for web applications that maintain session information.
- Protection: Provides protection against certain types of threats, like DDoS attacks.
Question: What is clustered database environment, how do you expand this if there is a need?
Answer: A clustered database environment involves the use of multiple servers or instances that appear to applications as a single database system. The primary goal is to ensure high availability. If one server or instance fails, the workload is rerouted to another server or instance. To expand a clustered database environment:
- Add Nodes: Introduce more servers or instances to the cluster, distributing the database workload further.
- Redistribute Data: In partitioned or sharded systems, redistribute data to take advantage of the new nodes.
- Update Cluster Configuration: Ensure the cluster management software recognizes and manages the new nodes.
- Rebalance Load Balancer (if used): If there's a load balancer in front of the cluster, its configuration might need updates to distribute traffic to the new nodes.
Question: What is Database Normalization?
Answer: Database normalization is the process of organizing the columns (attributes) and tables (relations) of a relational database to reduce data redundancy and improve data integrity. It involves decomposing larger tables into smaller, less redundant tables and linking them using foreign keys. Normalization is done in stages called normal forms, with each successive form addressing a certain kind of redundancy or structural issue.
Question: Describe OSI Layer-3 in detail?
Answer: OSI Layer-3 is known as the Network Layer. Its main functionalities and characteristics include:
- Routing: Determines the best path to route packets from the source to the destination across the network. Routers operate at this layer.
- Logical Addressing: Every device on a network has a logical address, typically known as an IP address, to uniquely identify it.
- Path Selection: Based on factors like routing protocols, policies, or metrics, the best path for data transfer is chosen.
- Fragmentation and Reassembly: If a packet is too large for a downstream network, it's fragmented into smaller packets. These are then reassembled at the destination.
- Connectionless Communication: The Network Layer primarily uses connectionless communication, meaning each packet is treated independently from others.
- Error Handling and Diagnostics: Protocols at this layer can identify issues with packet delivery and might initiate diagnostic functions like ICMP (Internet Control Message Protocol) for troubleshooting.
Question: Can you describe what happens when you try to connect to a website using a browser?
Answer: When you try to connect to a website using a browser:
- URL Parsing: The browser parses the URL to determine the protocol (e.g., HTTP or HTTPS), domain name, path, and other components.
- DNS Resolution: The browser checks if it has the IP address for the domain in its cache. If not, it queries a DNS server to resolve the domain name to an IP address.
- TCP Connection: The browser initiates a TCP connection with the server using the Three-Way Handshake.
- SSL/TLS Handshake: If HTTPS is used, there's an additional handshake for the SSL/TLS encryption setup.
- HTTP Request: The browser sends an HTTP request to the server, asking for the desired webpage.
- Server Response: The server processes the request and sends back an HTTP response containing the webpage's content or an error message.
- Rendering: The browser processes the received data, executing scripts, styling with CSS, and rendering the webpage on your screen.
- Additional Resource Requests: For embedded resources (images, CSS, JavaScript, etc.), additional HTTP requests are made.
- Connection Termination: After the transaction, the browser and server terminate the TCP connection, possibly with a Four-Way Handshake if the connection isn't kept alive for further requests.
- Displaying Content: The browser displays the webpage content, making additional requests as needed for dynamic content or user interactions.
Question: What is RAID?
Answer: RAID stands for Redundant Array of Independent Disks. It's a technology used to combine multiple hard drives into a single unit, referred to as an array. The purpose of RAID is to improve performance, increase storage capacity, and provide redundancy to prevent data loss in case of a drive failure.
Question: What all are the RAID types?
Answer: There are several RAID levels, each with its own method of data protection or performance improvement. Some common RAID levels include:
- RAID 0 (Striping): Data is split across all disks in the array. It improves performance but offers no redundancy.
- RAID 1 (Mirroring): Data is duplicated on two drives. It offers redundancy at the cost of halved storage capacity.
- RAID 5 (Distributed Parity): Data and parity are striped across three or more drives. It offers both performance and redundancy.
- RAID 6 (Double Parity): Similar to RAID 5 but with double parity, allowing it to handle two simultaneous disk failures.
- RAID 10 (1+0): A combination of RAID 1 and RAID 0, offering both performance and redundancy.
- RAID 50 and RAID 60: These are combinations of RAID 5 or 6 with RAID 0, respectively.
There are other specialized RAID levels as well, but these are the most commonly used.
Question: What is RAID-10?
Answer: RAID-10, also known as RAID 1+0, is a combination of RAID 1 (Mirroring) and RAID 0 (Striping). It requires a minimum of four disks. In RAID-10, data is striped across multiple mirrored pairs. This means that each piece of data is written to two disks simultaneously (mirroring) and then this mirrored data is striped across the RAID array. RAID-10 offers both high performance (due to striping) and redundancy (due to mirroring). It can withstand the failure of one disk in each mirrored pair without data loss.
Question: Design a 3-tier web application which is required heavy read like 1 million reads concurrently?
Answer: Designing a 3-tier web application for heavy read concurrency involves optimizing each tier for read operations.
Presentation Tier (Front-end):
- Use Content Delivery Networks (CDN) to cache and deliver static resources like images, CSS, and JavaScript. This reduces the load on your servers and provides faster content delivery to users.
- Implement aggressive caching strategies to reduce the need for repeated data fetches.
Logic Tier (Application Server):
- Use load balancers to distribute incoming requests across multiple application servers, ensuring high availability and fault tolerance.
- Optimize application code for read-heavy operations, avoiding unnecessary write or update operations.
- Implement caching solutions like Redis or Memcached to cache frequent query results, reducing direct hits to the database.
Data Tier (Database):
- Opt for a read-optimized database. Solutions like Amazon Aurora or Google Cloud Spanner can handle heavy read workloads.
- Use read replicas to distribute the read load. Requests can be sent to these replicas instead of the primary database, ensuring the primary database isn't overwhelmed.
- Implement database caching to store frequent query results.
- Regularly optimize and index the database to ensure queries run efficiently.
- Consider using NoSQL databases like Cassandra or MongoDB for specific use cases, as they can handle high read rates effectively.
Question: What is hot standby in Database?
Answer: A "hot standby" refers to a backup database system that is fully operational and can take over immediately in the event of the primary database system failing. The hot standby system remains in sync with the primary database, typically through real-time data replication. If the primary system fails, the hot standby can be promoted to act as the primary, ensuring minimal downtime and data loss. This approach is often used in high-availability architectures to ensure uninterrupted access to critical data.
Question: How would you create a clustered database environment?
Answer: Creating a clustered database environment involves several steps:
- Assessment: Evaluate the current database workload, data size, and performance metrics.
- Choose Database Software: Some databases have native clustering support, like MySQL Cluster, Oracle RAC, or Microsoft SQL Server Always On Availability Groups.
- Hardware Configuration: Ensure that the servers are equipped with sufficient RAM, CPU, and fast storage to handle the database workload.
- Network Configuration: Set up a fast, low-latency network to connect cluster nodes.
- Install Database Software: Install the chosen database software on all nodes.
- Configure Replication: For some clustered solutions, data replication between nodes is required. Set up synchronous or asynchronous replication based on needs.
- Set Up Load Balancing: Use database load balancers or proxies, such as ProxySQL or HAProxy, to distribute queries among cluster nodes.
- Failover Configuration: Ensure automatic failover mechanisms are in place for high availability.
- Testing: Simulate failures to test failover, data integrity, and performance.
Question: What is block storage and how it differs from object storage?
Answer:
- Block Storage: Block storage divides data into blocks, and each block is assigned a unique identifier. The blocks are stored in SANs (Storage Area Networks) and are often used for storage-intensive applications like databases. Block storage provides low latency and high performance.
Key Characteristics: High performance, fine-grained control, commonly used for databases and file systems.
- Object Storage: Object storage stores data as objects, where each object contains the data, metadata, and a globally unique identifier. Object storage systems, like Amazon S3 or OpenStack Swift, are highly scalable and are designed for large amounts of unstructured data, like backups or multimedia content.
Key Characteristics: Highly scalable, metadata included, suited for unstructured data, often used for backups, and web content. The main differences include their architecture, performance profile, scalability, and use cases.
Question: How would you horizontally scale a multi-tier web application?
Answer:
- Load Balancing: Implement load balancers to distribute traffic across multiple instances of application servers.
- Stateless Application Servers: Ensure application servers are stateless so any server can handle any request.
- Database Scaling: Use master-slave replication, sharding, or distributed databases to horizontally scale the database tier.
- Caching: Implement distributed caching solutions like Redis or Memcached to reduce database load.
- Content Delivery Network (CDN): Use CDNs to cache static assets closer to users, reducing the load on the origin server.
- Microservices: Decompose the application into microservices, allowing individual components to scale independently based on demand.
- Auto-scaling: Use cloud-based auto-scaling to automatically add or remove resources based on traffic.
Question: What are the 3-tiers of Web Application?
Answer:
- Presentation Tier (Front-end): This is the user interface of the application. It's where users interact with the application, typically through a web browser. It presents data to the user and takes user input.
- Logic Tier (Application Server): This tier processes the business logic of the application. It interacts with the database to fetch, process, and store data. It also communicates with the front-end to send and receive data.
- Data Tier (Database): This is where the application's data is stored and retrieved. It's responsible for ensuring data integrity, consistency, and persistence.
Question: What are the tools used for data replication?
Answer:
RDBMS Tools: Many relational databases offer native replication solutions:
- MySQL: Master-Slave Replication, Group Replication.
- PostgreSQL: Streaming Replication, Logical Replication.
- Microsoft SQL Server: Always On Availability Groups, Transactional Replication.
- Oracle: Oracle Data Guard, GoldenGate.
2. NoSQL Replication Tools: NoSQL databases often have built-in replication mechanisms:
- MongoDB: Replica Sets.
- Cassandra: Multi-node replication based on the Gossip protocol.
- Redis: Master-Slave Replication, Sentinel.
3. Middleware Tools: Tools that sit between the application and the database to manage replication:
- Kafka: Can be used for replicating data across systems in real-time.
- Tungsten Replicator: Offers replication between various databases.
4. Cloud-specific Tools: Cloud providers often have tools for replicating data within and across regions:
- AWS: Database Migration Service (DMS), Aurora Replication
- Azure: Azure SQL Data Sync
- Google Cloud: Cloud Spanner's inter-region replication.
Question: Can you tell me the process, about setting up a new Web Server?
Answer: Setting up a new web server involves several steps:
- Hardware/Cloud Provider Selection: Choose an appropriate server or cloud provider based on the requirements of the website (traffic, resources, scalability).
- Operating System Installation: Install a suitable OS, commonly Linux distributions like Ubuntu, CentOS, or Windows Server.
- Web Server Installation: Install a web server software like Apache, Nginx, or Microsoft's IIS.
- Configuration:
- Configure server settings (e.g., ports, virtual hosts, server blocks).
- Optimize for performance (e.g. , enabling compression, setting cache headers).
- Set up security features (e.g., configuring firewalls, installing SSL certificates for HTTPS).
- Database Setup (if required): Install and configure a database like MySQL, PostgreSQL, or MongoDB.
- Deploy Website/Application: Upload the website files or application code to the server.
- DNS Configuration: Update the domain name settings to point to the new server's IP address.
- Monitoring and Maintenance: Install monitoring tools to keep track of server performance and uptime. Regularly update and patch the software.
Question: What is a NoSQL database?
Answer: NoSQL database, or "Not Only SQL," is a type of database that provides a way to store and retrieve data that is modeled in means other than the tabular relations used in relational databases (RDBMS). NoSQL databases are often used for big data and real-time applications. They can be classified into several types:
- Document databases (e.g., MongoDB): Store data in document-like structures.
- Columnar databases (e.g., Cassandra, HBase): Store data in columns instead of rows.
- Key-Value stores (e.g., Redis, DynamoDB): Use a simple key-value method to store data.
- Graph databases (e.g. , Neo4j): Designed to store relationships between data points.
Question: Describe what is done in OSI Layer-2?
Answer: OSI Layer-2, also known as the Data Link Layer, is responsible for:
- Frame Creation: Encapsulating data from the Network Layer (Layer 3) into frames.
- Physical Addressing: Uses MAC (Media Access Control) addresses to uniquely identify devices on a local network.
- Error Detection: Identifies and possibly corrects errors that may occur in the Physical Layer (Layer 1) using techniques like CRC (Cyclic Redundancy Check).
- Switching: Layer-2 switches operate at this layer to forward frames based on MAC addresses.
- Flow Control: Ensures data is sent at a rate the receiver can handle.
- Logical Link Control (LLC): Helps with flow control and frame synchronization.
Question: What is the difference between TCP and UDP?
Answer:
TCP (Transmission Control Protocol):
- Connection-Oriented: Requires a connection setup with a three-way handshake before data transfer.
- Reliable: Ensures data delivery and automatically resends packets if lost.
- Ordered: Data packets are re-ordered in the sequence they were sent.
- Flow Control: Adjusts data flow to prevent overwhelming receiving devices.
- Overhead: Due to its features, it has a higher overhead than UDP.
UDP (User Datagram Protocol):
- Connectionless: Does not establish a connection before sending data.
- Unreliable: Does not guarantee data delivery or order.
- Low Overhead: Has less overhead as there's no connection setup, teardown, or error recovery.
- Use Cases: Often used for streaming, broadcasting, and tasks where low latency is more important than reliability.
Question: What is the difference between multicast and unicast?
Answer:
- Unicast: It is the sending of information packets to a single destination. A one-to-one communication. It involves direct communication between the sender and the single receiver.
- Multicast: It is the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once and create copies only when the links to the destinations split. A one-to-many or many-to-many communication.
Question: Can you describe the TCP model?
Answer: The TCP/IP model, also known as the Internet Protocol Suite, is the conceptual framework for the protocols used by the Internet. It has four layers:
Application Layer: This is the topmost layer, which represents the level at which applications access network services. This layer combines the responsibilities of the OSI model's Application, Presentation, and Session layers. Protocols like HTTP, FTP, SMTP, and DNS operate at this layer.
Transport Layer: Responsible for end-to-end communication and data flow control. The main protocols operating at this layer are TCP (Transmission Control Protocol), which is connection-oriented and guarantees the delivery of packets, and UDP (User Datagram Protocol), which is connectionless and does not guarantee packet delivery.
Internet Layer: This layer is responsible for packet forwarding, including routing through different networks and IP addressing. The main protocol in this layer is the IP (Internet Protocol), but others include ICMP (Internet Control Message Protocol) and IGMP (Internet Group Management Protocol).
Link Layer (or Network Interface Layer): This layer deals with protocols related to the local network segment. It includes hardware addressing and error detection/correction. Ethernet, Wi-Fi, and PPP are examples of protocols and technologies operating at this layer.
Question: Describe the scaling process?
Answer: Scaling is the process of adding resources to increase the capacity of a system. It's commonly referred to in the context of web applications and databases. There are two primary methods:
Horizontal Scaling (Scale Out): Involves adding more nodes to the system. For instance, adding more servers to distribute the load. This is often seen in distributed systems like cloud environments where new instances can be launched to handle increased traffic.
Vertical Scaling (Scale Up): Involves adding more resources to an existing node. This could mean increasing the RAM, CPU, or storage of an existing server. It has limitations based on the hardware's maximum capacity.
The scaling process usually involves:
- Monitoring: Continuously monitoring system performance and throughput.
- Threshold Identification: Setting up predefined thresholds for when scaling should occur.
- Automation: Using tools or scripts to automatically scale resources based on the thresholds.
- Optimization: Regularly optimizing application code and database queries to ensure efficient resource utilization.
- Testing: Conducting load and stress testing to validate scaling strategies.
Question: Explain the difference between Asymmetric and Symmetric encryption?
Answer:
Symmetric Encryption:
- Single Key: The same key is used for both encryption and decryption.
- Speed: Generally faster than asymmetric encryption.
- Risk: If the key is lost or compromised, the data is at risk.
- Examples: AES, DES, 3DES, and RC4.
Asymmetric Encryption:
- Key Pair: Uses two keys - a public key for encryption and a private key for decryption.
- Security: The public key can be shared openly without compromising data security. Only the private key (which is kept secret) can decrypt the data.
- Usage: Commonly used for secure data transmission, digital signatures, and SSL/TLS.
- Examples: RSA, DSA, and Elliptic Curve Cryptography (ECC).
Question: What is the DataLake and what its use?
Answer: A Data Lake is a storage system or repository that can store vast amounts of raw data in its native format until it is needed. The data can be structured, semi-structured, or unstructured.
Uses of Data Lake:
- Big Data & Advanced Analytics: Allows for the processing and analysis of large datasets using tools like Hadoop or Spark.
- Real-time Analytics: Can store and analyze data in real-time, offering insights faster than traditional databases.
- Machine Learning & AI: Provides vast amounts of data that can be used for training machine learning models.
- Data Exploration: Allows data scientists and analysts to explore raw data to identify patterns or insights.
- Integration with Data Warehouses: Can be used in tandem with a data warehouse to store raw data, which can be later refined and loaded into the warehouse for structured querying.
Question: What is the CDN and why you use it?
Answer: A CDN (Content Delivery Network) is a distributed system of servers that deliver web content and resources to users based on their geographic location, the origin of the web page, and the content delivery server.
Reasons to use a CDN:
- Speed: Reduces the physical distance between the user and the server, resulting in faster content loading times.
- Reduced Load on Origin Server: Distributes user requests across multiple servers, preventing any single server from getting overwhelmed.
- Increased Availability & Redundancy: If one server is unavailable, the CDN redirects traffic to the next nearest server.
- Reduced Bandwidth Costs: Through caching and optimization techniques, CDNs can reduce the amount of data an origin server must provide.
- Enhanced Security: CDNs can provide DDoS protection and secure data transmission.
Question: What is the reason you want to use a CDN for an Object and it should have zero TTL?
Answer: Using a CDN with a zero Time-To-Live (TTL) for an object means that the CDN will always fetch the latest version of that object from the origin server on every request. Reasons for using zero TTL include:
- Real-time Data Requirements: If the content changes frequently and users need to access the most recent version instantly.
- Avoid Stale Data: To prevent serving outdated or cached content.
- Compliance or Regulatory Requirements: Some data might have regulations that mandate the latest version to be served.
- Debugging: When troubleshooting, it might be helpful to ensure the latest content is always fetched.
Question: What is the use of Hadoop?
Answer: Hadoop is an open-source framework that facilitates distributed processing of large datasets across clusters of computers using simple programming models.
Uses of Hadoop:
- Big Data Processing: Can handle and analyze massive amounts of data efficiently.
- Scalability: New nodes can be added to the system easily without affecting the dataset or the processing.
- Fault Tolerance: Data is automatically replicated across nodes. If a node fails, data can be recovered from other nodes.
- Cost-effective: Uses commodity hardware, making it cheaper compared to traditional databases for massive data storage.
- Data Locality: Moves computation to data rather than the other way around, reducing data transfer and increasing processing speed.
Question: What is the IPSec?
Answer: IPSec (Internet Protocol Security) is a suite of protocols that ensures the authentication, integrity, and encryption of IP packets. It operates at the IP layer and is commonly used for VPNs (Virtual Private Networks) and securing IP traffic.
IPSec offers:
- Authentication Headers (AH): Provides packet-level authentication.
- Encapsulating Security Payloads (ESP): Provides encryption, authentication, and integrity.
- Security Associations (SA): Defines the parameters for how communication between two parties will be secured.
- Key Exchange: Typically done with the Internet Key Exchange (IKE) protocol.
Question: What is the SSL VPN?
Answer: SSL VPN (Secure Sockets Layer Virtual Private Network) is a type of VPN that uses the SSL protocol to secure and encrypt communication between the user's device and the VPN server. Unlike traditional IP-based VPNs, SSL VPNs are accessed via a web browser.
Advantages of SSL VPN:
- Clientless Access: Users can access the VPN via a web browser without the need to install a software client.
- Granular Access Control: Allows for fine-tuned access to specific parts of a network.
- Cross-platform Compatibility: Can be accessed from any device with a web browser.
- Secure Connection: Uses SSL/TLS to encrypt the data ensuring that the data remains confidential and intact.
Question: What is the difference between IPSec and SSL VPN?
Answer: IPSec and SSL VPN are both protocols used to establish secure connections, but they differ in their applications, implementation, and mechanisms. Here's a comparison:
Connection Level:
- IPSec: Operates at the IP layer and secures all data that is sent from the source to the destination. It's often used for site-to-site VPNs.
- SSL VPN: Operates at the application layer and secures specific application sessions. It's commonly used for remote access.
Client Requirement:
- IPSec: Requires a specialized client software to establish a connection.
- SSL VPN: Typically does not require any special client software as it can be accessed through a web browser (clientless).
Granular Access:
- IPSec: Often provides access to the entire network.
- SSL VPN: Can provide fine-grained access to specific applications or sections of a network.
Ease of Use:
- IPSec: Configuration can be more complex due to its operating level and broader access.
- SSL VPN: Simpler to set up for remote access and is more user-friendly for end-users accessing via a browser.
Port Usage:
- IPSec: Uses specific ports, which might be blocked by some firewalls.
- SSL VPN: Uses standard SSL/TLS ports (e.g., port 443), which are usually open on most firewalls.
Question: What is the reason or where you would prefer NoSQL database over Relational Database?
Answer: NoSQL databases are preferred over Relational Databases (RDBMS) in certain situations due to their flexibility, scalability, and performance characteristics. Some reasons include:
- Scalability: NoSQL databases can horizontally scale out by adding more servers to the system, making them suitable for big data and high-velocity applications.
- Flexible Schema: NoSQL databases allow for flexible data models which can be easily modified without affecting existing data.
- Diverse Data Types: Ideal for semi-structured or unstructured data like JSON, XML, etc.
- Low Latency: Some NoSQL databases can provide low latency read and write operations which are useful for real-time applications.
- High Throughput: Suitable for applications that require massive read and write operations.
Question: Name five Linux commands which have 5 or more letters?
Answer:
- ‘mkdir’ (to create a directory)
- ‘rmdir’ (to remove a directory)
- ‘chmod’ (to change file permissions)
- ‘chown’ (to change file owner)
- ‘ifconfig’ (to configure a network interface)
Question: Can you describe a Web Application and all its components?
Answer: A web appl ication is a software program that runs on a web server and is accessed through a web browser over the Internet. Components include:
- User Interface: The frontend, including HTML, CSS, and JavaScript, which determines how the application looks and interacts with users.
- Application Logic: Backend code, written in languages like Python, Java, or PHP, that handles data processing, business logic, and interacts with databases.
- Database: Where data is stored, retrieved, and updated. Examples include MySQL, PostgreSQL, and MongoDB.
- Web Server: Software that serves web pages to users. Examples include Apache, Nginx, and IIS.
- Middleware: Software components that provide services to integrate different parts of the web application, such as authentication, session management, and caching.
- APIs: Interfaces that allow the web application to communicate with other services or applications.
- Hosting Environment: The infrastructure where the web application is hosted, such as cloud providers, dedicated servers, or shared hosting.
Question: Can you give a use case where you would use TCP and UDP?
Answer: TCP (Transmission Control Protocol): Ensures that all sent packets reach the destination in the correct order.
Use Case: File transfer where integrity and reliability are paramount, such as downloading a software update or accessing a website where the complete and ordered retrieval of all data is essential.
UDP (User Datagram Protocol): Sends packets without establishing a connection and does not guarantee packet delivery or order.
Use Case: Streaming services like online video or online gaming where real-time data transfer is more important than ensuring every single packet is received. If a few packets are lost in transit, it's more acceptable than introducing latency.
Question: What is RTO and RPO?
Answer: RTO (Recovery Time Objective) is the targeted duration of time and a service level within which a business process must be restored after a disaster in order to avoid unacceptable consequences associated with a break in continuity.
Question: What is ARP?
Answer: ARP (Address Resolution Protocol) is a protocol used in the IP network layer for mapping an IP address to a physical machine address that is recognized in the local network. It is crucial for IP operations as it facilitates the communication between Ethernet and IP addresses on a local area network.
Question: Design a 3-tier web application, where it should be able to support 1 million users simultaneously. Also, you have to make sure that the website is highly available? You will be asked various questions based on this design.
Answer: A 3-tier web application typically consists of the presentation layer, application layer, and data layer.
- Presentation Layer: This is where the end users interact. Use a global Content Delivery Network (CDN) to serve static content, ensuring faster load times and reducing load on the main servers. Employ a load balancer (e.g., AWS ELB) to distribute incoming traffic among multiple application servers.
- Application Layer: Deploy the application on multiple servers across different availability zones or even regions. Use auto-scaling to handle spikes in traffic. Statelessness is important to ensure any server can handle any request. For session management, use a distributed cache or a service like Redis or Memcached.
- Data Layer: Use a distributed database system that can handle a high number of IOPS and has replication across multiple zones/regions for high availability. Consider databases like Cassandra, Amazon DynamoDB, or even sharded relational databases. Regularly backup data and have a failover mechanism in place.
Ensure that the entire infrastructure is monitored with adequate logging and alerting mechanisms. Implement health checks to ensure high availability. Data security and regular vulnerability assessments are also crucial.
Question: What is OSI Model and describe each layer in it?
Answer: The OSI (Open Systems Interconnection) Model is a conceptual framework used to understand how different networking protocols interact across networks. The model consists of seven layers:
- Physical Layer: Deals with the physical connection between devices. It defines the hardware elements involved, such as cables, switches, and NICs.
- Data Link Layer: Responsible for creating a reliable link between two directly connected nodes. It provides addressing via MAC addresses and error correction.
- Network Layer: Determines the best path to route data from the source to the destination using logical addressing (like IP addresses).
- Transport Layer: Ensures reliable data transfer between two devices on a network. It uses ports to distinguish different services and can break data into chunks or segments for transmission.
- Session Layer: Establishes, maintains, and terminates connections (sessions) between applications on different devices.
- Presentation Layer: Transforms data from one presentation format to another. It deals with data compression, encryption, and translation services.
- Application Layer: The interface between the networking stack and end-user applications. It provides network services to applications and user processes.
Question: What is the LAMP stack?
Answer: The LAMP stack is an acronym for a popular set of open-source software used to get web servers up and running. The components of the LAMP stack are:
- Linux: The operating system.
- Apache: The web server software.
- MySQL: The relational database management system.
- PHP: The programming language used for web development (though it can also stand for Perl or Python).
Together, they provide a proven set of software for delivering high-performance web applications.
Question: What is WAF and how it differs from the Firewall?
Answer: WAF (Web Application Firewall) is a specific type of firewall that monitors, filters, and blocks HTTP traffic to and from web applications. It specifically focuses on protecting web applications by inspecting HTTP/HTTPS traffic to prevent web application attacks, such as SQL injection, cross-site scripting (XSS), and more. A traditional firewall, on the other hand, focuses on controlling network traffic based on IP addresses, ports, and protocols. In essence, while both provide security, WAF protects at the application layer (Layer 7 of OSI Model), and traditional firewalls operate mainly at the network layer.
Question: What is the difference between container and virtual machine, what is better in which situation?
Answer: A container is a lightweight, stand-alone executable package that includes everything needed to run a piece of software, including the code, runtime, system tools, and libraries. Containers virtualize the OS, sharing the same OS kernel, while isolating the application processes from each other. Docker is a popular containerization platform.
Virtual Machines (VMs) virtualize the entire hardware to run multiple instances of full-fledged OS. Each VM includes both a full copy of an OS, a virtual copy of all the hardware that the OS needs to run, and an application.
Question: When to use Containers?
Answer:
- When you need faster start-up times.
- When you want more efficient utilization of underlying resources.
- For microservice architectures.
- When you need consistency across multiple environments.
Question: When to use VMs?
Answer:
- When running applications that require all the resources and functionality of an entire OS.
- When you need to run multiple applications on servers with different OS requirements.
- When a higher degree of isolation is required.
Question: What is the difference between cluster and mirroring?
Answer: In the context of databases:
- Cluster: A cluster consists of two or more servers that work together to provide high availability, load balancing, and failover capabilities. Clustering distributes the workload among all servers, maximizing throughput and capacity. If one server fails, the workload is rerouted to the remaining servers.
- Mirroring: Mirroring is a solution to provide a high-availability data protection by creating an exact replica of a database on another server. If the primary database becomes unavailable, the system can switch to the mirrored database, ensuring continuity of operations. Mirroring typically involves two servers only: a principal server and a mirrored server.
Question: What is the SQL and NoSQL database, can you give me the example in which situation you would prefer NoSQL over SQL?
Answer:
- SQL (Relational Databases): These are traditional databases that use structured query language (SQL) for defining and manipulating data. Data is stored in rows and columns in tables. Examples include MySQL, PostgreSQL, and Microsoft SQL Server.
- NoSQL: Refers to non-relational databases that do not use SQL as their primary query language. Data can be stored in various ways: key-value pairs, wide-column stores, document stores, or graph databases. Examples include MongoDB (document store), Cassandra (wide-column store), and Redis (key-value store).
Question: When to prefer NoSQL over SQL?
Answer:
- Handling large volumes of data with diverse structures.
- Need for flexible schema or schema-less data model.
- Quick and iterative development cycles.
- High-speed, scalable, and distributed systems, like real-time analytics.
- When dealing with hierarchical or multi-valued data, as in the case of JSON-like documents.
Question: What is horizontal scaling and vertical scaling?
Answer:
- Horizontal Scaling (Scale Out): This involves adding more servers to the existing pool or cluster to distribute the load, essentially scaling out by increasing the number of nodes in the system. This type of scaling offers high availability as there's no single point of failure.
- Vertical Scaling (Scale Up): Involves adding more resources (CPU, RAM, storage) to an existing server. It's about making a single node in the system more powerful. However, there's a limit to how much you can scale up due to hardware constraints and potential single points of failure.
Question: What is monolithic architecture?
Answer: Monolithic architecture refers to a software design where all the components of the application (like user interface, data access code, and business logic) are bundled together tightly into a single codebase and run as a single service. Changes or updates to any component often require building and deploying the entire application anew. Monolithic applications are typically easier to develop and test initially, but they can become complex and hard to manage as they grow.
Question: What is microservice based architecture and how it is different from the monolithic architecture?
Answer: Microservice architecture is a design approach where an application is broken down into a collection of loosely coupled, independently deployable services. Each microservice usually corresponds to a single business capability and communicates with others over a network, often using HTTP/REST or message queues. The key differences from monolithic architecture are:
- Modularity: Microservices are modular and independent, while monoliths are typically a single, tightly-integrated unit.
- Scalability: Each microservice can be scaled independently based on demand, whereas in monolithic architectures, the entire application must be scaled.
- Deployment: Changes in one microservice can be deployed independently without affecting others, whereas changes in a monolithic application typically require the whole application to be rebuilt and redeployed.
- Technology Stack: Different microservices can use different technologies, libraries, and databases, but monolithic applications typically have a single unified technology stack.
Question: What is Data Warehouse and how it differs from Database?
Answer: A Data Warehouse is a large, centralized repository of data that is specifically designed for query and analysis. It aggregates data from multiple sources, making it easier for businesses to derive insights. Differences from a standard operational database include:
- Purpose: Databases are designed for regular transactional operations (OLTP - Online Transaction Processing), while data warehouses are designed for analytical processing (OLAP - Online Analytical Processing).
- Design: Data warehouses often use denormalized data structures to optimize query performance, whereas operational databases often use normalized structures to optimize update/insert performance and minimize data redundancy.
- Size: Data warehouses usually store a larger amount of historical data compared to databases.
- Integration: Data warehouses typically pull data from various sources and provide a unified view.
Question: What do you mean by hypervisor?
Answer: A hypervisor, also known as a virtual machine monitor (VMM), is software, firmware, or hardware that creates and runs virtual machines (VMs). It allows multiple operating systems to share a single hardware host. There are two main types of hypervisors:
- Type 1 (Bare Metal): Runs directly on the host's hardware to control the hardware and manage guest operating systems. Examples include VMware vSphere/ESXi, Microsoft Hyper-V, and Xen.
- Type 2 (Hosted): Runs on a conventional operating system (the host OS) as a software layer. Examples include VMware Workstation and Oracle VirtualBox.
Question: Explain the usage of OSI Layer-4 and OSI Layer-7?
Answer:
- OSI Layer-4 (Transport Layer): This layer ensures the reliable transmission of data segments between points on a network, including segmentation, acknowledgment, and error recovery. Protocols like TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) operate at this layer. It's also responsible for end-to-end flow control and establishes, maintains, and terminates connections.
- OSI Layer-7 (Application Layer): This is the top layer of the OSI Model and directly interacts with end-user applications. It provides network services to application processes. Common protocols at this layer include HTTP, FTP, SMTP, and more. It's responsible for data formatting, encryption, and compression, and also ensures that the sender and receiver are communicating in a compatible format.
Question: Can you explain the Load Balancer working?
Answer: A Load Balancer is a device or service that distributes incoming network traffic across multiple servers to ensure no single server is overwhelmed with too much traffic. This helps maximize responsiveness and availability. The working of a load balancer includes:
- Traffic Distribution: Based on algorithms like round robin, least connections, or response time, it distributes client requests across multiple servers.
- Health Checks: Periodically checks the health of servers. If a server is found to be down or not responding, it stops sending traffic to that server until it's healthy again.
- SSL Termination: Handles the SSL handshake and decrypts incoming requests and encrypts responses, offloading the SSL overhead from the actual servers.
- Session Persistence: Ensures a client consistently connects to the same backend server, essential for web applications that maintain session information.
- Protection: Provides protection against certain types of threats, like DDoS attacks.
Question: What is clustered database environment, how do you expand this if there is a need?
Answer: A clustered database environment involves the use of multiple servers or instances that appear to applications as a single database system. The primary goal is to ensure high availability. If one server or instance fails, the workload is rerouted to another server or instance. To expand a clustered database environment:
- Add Nodes: Introduce more servers or instances to the cluster, distributing the database workload further.
- Redistribute Data: In partitioned or sharded systems, redistribute data to take advantage of the new nodes.
- Update Cluster Configuration: Ensure the cluster management software recognizes and manages the new nodes.
- Rebalance Load Balancer (if used): If there's a load balancer in front of the cluster, its configuration might need updates to distribute traffic to the new nodes.
Question: What is Database Normalization?
Answer: Database normalization is the process of organizing the columns (attributes) and tables (relations) of a relational database to reduce data redundancy and improve data integrity. It involves decomposing larger tables into smaller, less redundant tables and linking them using foreign keys. Normalization is done in stages called normal forms, with each successive form addressing a certain kind of redundancy or structural issue.
Question: Describe OSI Layer-3 in detail?
Answer: OSI Layer-3 is known as the Network Layer. Its main functionalities and characteristics include:
- Routing: Determines the best path to route packets from the source to the destination across the network. Routers operate at this layer.
- Logical Addressing: Every device on a network has a logical address, typically known as an IP address, to uniquely identify it.
- Path Selection: Based on factors like routing protocols, policies, or metrics, the best path for data transfer is chosen.
- Fragmentation and Reassembly: If a packet is too large for a downstream network, it's fragmented into smaller packets. These are then reassembled at the destination.
- Connectionless Communication: The Network Layer primarily uses connectionless communication, meaning each packet is treated independently from others.
- Error Handling and Diagnostics: Protocols at this layer can identify issues with packet delivery and might initiate diagnostic functions like ICMP (Internet Control Message Protocol) for troubleshooting.
Question: Can you describe what happens when you try to connect to a website using a browser?
Answer: When you try to connect to a website using a browser:
- URL Parsing: The browser parses the URL to determine the protocol (e.g., HTTP or HTTPS), domain name, path, and other components.
- DNS Resolution: The browser checks if it has the IP address for the domain in its cache. If not, it queries a DNS server to resolve the domain name to an IP address.
- TCP Connection: The browser initiates a TCP connection with the server using the Three-Way Handshake.
- SSL/TLS Handshake: If HTTPS is used, there's an additional handshake for the SSL/TLS encryption setup.
- HTTP Request: The browser sends an HTTP request to the server, asking for the desired webpage.
- Server Response: The server processes the request and sends back an HTTP response containing the webpage's content or an error message.
- Rendering: The browser processes the received data, executing scripts, styling with CSS, and rendering the webpage on your screen.
- Additional Resource Requests: For embedded resources (images, CSS, JavaScript, etc.), additional HTTP requests are made.
- Connection Termination: After the transaction, the browser and server terminate the TCP connection, possibly with a Four-Way Handshake if the connection isn't kept alive for further requests.
- Displaying Content: The browser displays the webpage content, making additional requests as needed for dynamic content or user interactions.
Question: What is RAID?
Answer: RAID stands for Redundant Array of Independent Disks. It's a technology used to combine multiple hard drives into a single unit, referred to as an array. The purpose of RAID is to improve performance, increase storage capacity, and provide redundancy to prevent data loss in case of a drive failure.
Question: What all are the RAID types?
Answer: There are several RAID levels, each with its own method of data protection or performance improvement. Some common RAID levels include:
- RAID 0 (Striping): Data is split across all disks in the array. It improves performance but offers no redundancy.
- RAID 1 (Mirroring): Data is duplicated on two drives. It offers redundancy at the cost of halved storage capacity.
- RAID 5 (Distributed Parity): Data and parity are striped across three or more drives. It offers both performance and redundancy.
- RAID 6 (Double Parity): Similar to RAID 5 but with double parity, allowing it to handle two simultaneous disk failures.
- RAID 10 (1+0): A combination of RAID 1 and RAID 0, offering both performance and redundancy.
- RAID 50 and RAID 60: These are combinations of RAID 5 or 6 with RAID 0, respectively.
There are other specialized RAID levels as well, but these are the most commonly used.
Question: What is RAID-10?
Answer: RAID-10, also known as RAID 1+0, is a combination of RAID 1 (Mirroring) and RAID 0 (Striping). It requires a minimum of four disks. In RAID-10, data is striped across multiple mirrored pairs. This means that each piece of data is written to two disks simultaneously (mirroring) and then this mirrored data is striped across the RAID array. RAID-10 offers both high performance (due to striping) and redundancy (due to mirroring). It can withstand the failure of one disk in each mirrored pair without data loss.
Question: Design a 3-tier web application which is required heavy read like 1 million reads concurrently?
Answer: Designing a 3-tier web application for heavy read concurrency involves optimizing each tier for read operations.
Presentation Tier (Front-end):
- Use Content Delivery Networks (CDN) to cache and deliver static resources like images, CSS, and JavaScript. This reduces the load on your servers and provides faster content delivery to users.
- Implement aggressive caching strategies to reduce the need for repeated data fetches.
Logic Tier (Application Server):
- Use load balancers to distribute incoming requests across multiple application servers, ensuring high availability and fault tolerance.
- Optimize application code for read-heavy operations, avoiding unnecessary write or update operations.
- Implement caching solutions like Redis or Memcached to cache frequent query results, reducing direct hits to the database.
Data Tier (Database):
- Opt for a read-optimized database. Solutions like Amazon Aurora or Google Cloud Spanner can handle heavy read workloads.
- Use read replicas to distribute the read load. Requests can be sent to these replicas instead of the primary database, ensuring the primary database isn't overwhelmed.
- Implement database caching to store frequent query results.
- Regularly optimize and index the database to ensure queries run efficiently.
- Consider using NoSQL databases like Cassandra or MongoDB for specific use cases, as they can handle high read rates effectively.
Question: What is hot standby in Database?
Answer: A "hot standby" refers to a backup database system that is fully operational and can take over immediately in the event of the primary database system failing. The hot standby system remains in sync with the primary database, typically through real-time data replication. If the primary system fails, the hot standby can be promoted to act as the primary, ensuring minimal downtime and data loss. This approach is often used in high-availability architectures to ensure uninterrupted access to critical data.
Question: How would you create a clustered database environment?
Answer: Creating a clustered database environment involves several steps:
- Assessment: Evaluate the current database workload, data size, and performance metrics.
- Choose Database Software: Some databases have native clustering support, like MySQL Cluster, Oracle RAC, or Microsoft SQL Server Always On Availability Groups.
- Hardware Configuration: Ensure that the servers are equipped with sufficient RAM, CPU, and fast storage to handle the database workload.
- Network Configuration: Set up a fast, low-latency network to connect cluster nodes.
- Install Database Software: Install the chosen database software on all nodes.
- Configure Replication: For some clustered solutions, data replication between nodes is required. Set up synchronous or asynchronous replication based on needs.
- Set Up Load Balancing: Use database load balancers or proxies, such as ProxySQL or HAProxy, to distribute queries among cluster nodes.
- Failover Configuration: Ensure automatic failover mechanisms are in place for high availability.
- Testing: Simulate failures to test failover, data integrity, and performance.
Question: What is block storage and how it differs from object storage?
Answer:
- Block Storage: Block storage divides data into blocks, and each block is assigned a unique identifier. The blocks are stored in SANs (Storage Area Networks) and are often used for storage-intensive applications like databases. Block storage provides low latency and high performance.
Key Characteristics: High performance, fine-grained control, commonly used for databases and file systems.
- Object Storage: Object storage stores data as objects, where each object contains the data, metadata, and a globally unique identifier. Object storage systems, like Amazon S3 or OpenStack Swift, are highly scalable and are designed for large amounts of unstructured data, like backups or multimedia content.
Key Characteristics: Highly scalable, metadata included, suited for unstructured data, often used for backups, and web content. The main differences include their architecture, performance profile, scalability, and use cases.
Question: How would you horizontally scale a multi-tier web application?
Answer:
- Load Balancing: Implement load balancers to distribute traffic across multiple instances of application servers.
- Stateless Application Servers: Ensure application servers are stateless so any server can handle any request.
- Database Scaling: Use master-slave replication, sharding, or distributed databases to horizontally scale the database tier.
- Caching: Implement distributed caching solutions like Redis or Memcached to reduce database load.
- Content Delivery Network (CDN): Use CDNs to cache static assets closer to users, reducing the load on the origin server.
- Microservices: Decompose the application into microservices, allowing individual components to scale independently based on demand.
- Auto-scaling: Use cloud-based auto-scaling to automatically add or remove resources based on traffic.
Question: What are the 3-tiers of Web Application?
Answer:
- Presentation Tier (Front-end): This is the user interface of the application. It's where users interact with the application, typically through a web browser. It presents data to the user and takes user input.
- Logic Tier (Application Server): This tier processes the business logic of the application. It interacts with the database to fetch, process, and store data. It also communicates with the front-end to send and receive data.
- Data Tier (Database): This is where the application's data is stored and retrieved. It's responsible for ensuring data integrity, consistency, and persistence.
Question: What are the tools used for data replication?
Answer:
RDBMS Tools: Many relational databases offer native replication solutions:
- MySQL: Master-Slave Replication, Group Replication.
- PostgreSQL: Streaming Replication, Logical Replication.
- Microsoft SQL Server: Always On Availability Groups, Transactional Replication.
- Oracle: Oracle Data Guard, GoldenGate.
2. NoSQL Replication Tools: NoSQL databases often have built-in replication mechanisms:
- MongoDB: Replica Sets.
- Cassandra: Multi-node replication based on the Gossip protocol.
- Redis: Master-Slave Replication, Sentinel.
3. Middleware Tools: Tools that sit between the application and the database to manage replication:
- Kafka: Can be used for replicating data across systems in real-time.
- Tungsten Replicator: Offers replication between various databases.
4. Cloud-specific Tools: Cloud providers often have tools for replicating data within and across regions:
- AWS: Database Migration Service (DMS), Aurora Replication
- Azure: Azure SQL Data Sync
- Google Cloud: Cloud Spanner's inter-region replication.
Question: Can you tell me the process, about setting up a new Web Server?
Answer: Setting up a new web server involves several steps:
- Hardware/Cloud Provider Selection: Choose an appropriate server or cloud provider based on the requirements of the website (traffic, resources, scalability).
- Operating System Installation: Install a suitable OS, commonly Linux distributions like Ubuntu, CentOS, or Windows Server.
- Web Server Installation: Install a web server software like Apache, Nginx, or Microsoft's IIS.
- Configuration:
- Configure server settings (e.g., ports, virtual hosts, server blocks).
- Optimize for performance (e.g. , enabling compression, setting cache headers).
- Set up security features (e.g., configuring firewalls, installing SSL certificates for HTTPS).
- Database Setup (if required): Install and configure a database like MySQL, PostgreSQL, or MongoDB.
- Deploy Website/Application: Upload the website files or application code to the server.
- DNS Configuration: Update the domain name settings to point to the new server's IP address.
- Monitoring and Maintenance: Install monitoring tools to keep track of server performance and uptime. Regularly update and patch the software.
Question: What is a NoSQL database?
Answer: NoSQL database, or "Not Only SQL," is a type of database that provides a way to store and retrieve data that is modeled in means other than the tabular relations used in relational databases (RDBMS). NoSQL databases are often used for big data and real-time applications. They can be classified into several types:
- Document databases (e.g., MongoDB): Store data in document-like structures.
- Columnar databases (e.g., Cassandra, HBase): Store data in columns instead of rows.
- Key-Value stores (e.g., Redis, DynamoDB): Use a simple key-value method to store data.
- Graph databases (e.g. , Neo4j): Designed to store relationships between data points.
Question: Describe what is done in OSI Layer-2?
Answer: OSI Layer-2, also known as the Data Link Layer, is responsible for:
- Frame Creation: Encapsulating data from the Network Layer (Layer 3) into frames.
- Physical Addressing: Uses MAC (Media Access Control) addresses to uniquely identify devices on a local network.
- Error Detection: Identifies and possibly corrects errors that may occur in the Physical Layer (Layer 1) using techniques like CRC (Cyclic Redundancy Check).
- Switching: Layer-2 switches operate at this layer to forward frames based on MAC addresses.
- Flow Control: Ensures data is sent at a rate the receiver can handle.
- Logical Link Control (LLC): Helps with flow control and frame synchronization.
Question: What is the difference between TCP and UDP?
Answer:
TCP (Transmission Control Protocol):
- Connection-Oriented: Requires a connection setup with a three-way handshake before data transfer.
- Reliable: Ensures data delivery and automatically resends packets if lost.
- Ordered: Data packets are re-ordered in the sequence they were sent.
- Flow Control: Adjusts data flow to prevent overwhelming receiving devices.
- Overhead: Due to its features, it has a higher overhead than UDP.
UDP (User Datagram Protocol):
- Connectionless: Does not establish a connection before sending data.
- Unreliable: Does not guarantee data delivery or order.
- Low Overhead: Has less overhead as there's no connection setup, teardown, or error recovery.
- Use Cases: Often used for streaming, broadcasting, and tasks where low latency is more important than reliability.
Question: What is the difference between multicast and unicast?
Answer:
- Unicast: It is the sending of information packets to a single destination. A one-to-one communication. It involves direct communication between the sender and the single receiver.
- Multicast: It is the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once and create copies only when the links to the destinations split. A one-to-many or many-to-many communication.
Question: Can you describe the TCP model?
Answer: The TCP/IP model, also known as the Internet Protocol Suite, is the conceptual framework for the protocols used by the Internet. It has four layers:
Application Layer: This is the topmost layer, which represents the level at which applications access network services. This layer combines the responsibilities of the OSI model's Application, Presentation, and Session layers. Protocols like HTTP, FTP, SMTP, and DNS operate at this layer.
Transport Layer: Responsible for end-to-end communication and data flow control. The main protocols operating at this layer are TCP (Transmission Control Protocol), which is connection-oriented and guarantees the delivery of packets, and UDP (User Datagram Protocol), which is connectionless and does not guarantee packet delivery.
Internet Layer: This layer is responsible for packet forwarding, including routing through different networks and IP addressing. The main protocol in this layer is the IP (Internet Protocol), but others include ICMP (Internet Control Message Protocol) and IGMP (Internet Group Management Protocol).
Link Layer (or Network Interface Layer): This layer deals with protocols related to the local network segment. It includes hardware addressing and error detection/correction. Ethernet, Wi-Fi, and PPP are examples of protocols and technologies operating at this layer.
Question: Describe the scaling process?
Answer: Scaling is the process of adding resources to increase the capacity of a system. It's commonly referred to in the context of web applications and databases. There are two primary methods:
Horizontal Scaling (Scale Out): Involves adding more nodes to the system. For instance, adding more servers to distribute the load. This is often seen in distributed systems like cloud environments where new instances can be launched to handle increased traffic.
Vertical Scaling (Scale Up): Involves adding more resources to an existing node. This could mean increasing the RAM, CPU, or storage of an existing server. It has limitations based on the hardware's maximum capacity.
The scaling process usually involves:
- Monitoring: Continuously monitoring system performance and throughput.
- Threshold Identification: Setting up predefined thresholds for when scaling should occur.
- Automation: Using tools or scripts to automatically scale resources based on the thresholds.
- Optimization: Regularly optimizing application code and database queries to ensure efficient resource utilization.
- Testing: Conducting load and stress testing to validate scaling strategies.
Question: Explain the difference between Asymmetric and Symmetric encryption?
Answer:
Symmetric Encryption:
- Single Key: The same key is used for both encryption and decryption.
- Speed: Generally faster than asymmetric encryption.
- Risk: If the key is lost or compromised, the data is at risk.
- Examples: AES, DES, 3DES, and RC4.
Asymmetric Encryption:
- Key Pair: Uses two keys - a public key for encryption and a private key for decryption.
- Security: The public key can be shared openly without compromising data security. Only the private key (which is kept secret) can decrypt the data.
- Usage: Commonly used for secure data transmission, digital signatures, and SSL/TLS.
- Examples: RSA, DSA, and Elliptic Curve Cryptography (ECC).
Question: What is the DataLake and what its use?
Answer: A Data Lake is a storage system or repository that can store vast amounts of raw data in its native format until it is needed. The data can be structured, semi-structured, or unstructured.
Uses of Data Lake:
- Big Data & Advanced Analytics: Allows for the processing and analysis of large datasets using tools like Hadoop or Spark.
- Real-time Analytics: Can store and analyze data in real-time, offering insights faster than traditional databases.
- Machine Learning & AI: Provides vast amounts of data that can be used for training machine learning models.
- Data Exploration: Allows data scientists and analysts to explore raw data to identify patterns or insights.
- Integration with Data Warehouses: Can be used in tandem with a data warehouse to store raw data, which can be later refined and loaded into the warehouse for structured querying.
Question: What is the CDN and why you use it?
Answer: A CDN (Content Delivery Network) is a distributed system of servers that deliver web content and resources to users based on their geographic location, the origin of the web page, and the content delivery server.
Reasons to use a CDN:
- Speed: Reduces the physical distance between the user and the server, resulting in faster content loading times.
- Reduced Load on Origin Server: Distributes user requests across multiple servers, preventing any single server from getting overwhelmed.
- Increased Availability & Redundancy: If one server is unavailable, the CDN redirects traffic to the next nearest server.
- Reduced Bandwidth Costs: Through caching and optimization techniques, CDNs can reduce the amount of data an origin server must provide.
- Enhanced Security: CDNs can provide DDoS protection and secure data transmission.
Question: What is the reason you want to use a CDN for an Object and it should have zero TTL?
Answer: Using a CDN with a zero Time-To-Live (TTL) for an object means that the CDN will always fetch the latest version of that object from the origin server on every request. Reasons for using zero TTL include:
- Real-time Data Requirements: If the content changes frequently and users need to access the most recent version instantly.
- Avoid Stale Data: To prevent serving outdated or cached content.
- Compliance or Regulatory Requirements: Some data might have regulations that mandate the latest version to be served.
- Debugging: When troubleshooting, it might be helpful to ensure the latest content is always fetched.
Question: What is the use of Hadoop?
Answer: Hadoop is an open-source framework that facilitates distributed processing of large datasets across clusters of computers using simple programming models.
Uses of Hadoop:
- Big Data Processing: Can handle and analyze massive amounts of data efficiently.
- Scalability: New nodes can be added to the system easily without affecting the dataset or the processing.
- Fault Tolerance: Data is automatically replicated across nodes. If a node fails, data can be recovered from other nodes.
- Cost-effective: Uses commodity hardware, making it cheaper compared to traditional databases for massive data storage.
- Data Locality: Moves computation to data rather than the other way around, reducing data transfer and increasing processing speed.
Question: What is the IPSec?
Answer: IPSec (Internet Protocol Security) is a suite of protocols that ensures the authentication, integrity, and encryption of IP packets. It operates at the IP layer and is commonly used for VPNs (Virtual Private Networks) and securing IP traffic.
IPSec offers:
- Authentication Headers (AH): Provides packet-level authentication.
- Encapsulating Security Payloads (ESP): Provides encryption, authentication, and integrity.
- Security Associations (SA): Defines the parameters for how communication between two parties will be secured.
- Key Exchange: Typically done with the Internet Key Exchange (IKE) protocol.
Question: What is the SSL VPN?
Answer: SSL VPN (Secure Sockets Layer Virtual Private Network) is a type of VPN that uses the SSL protocol to secure and encrypt communication between the user's device and the VPN server. Unlike traditional IP-based VPNs, SSL VPNs are accessed via a web browser.
Advantages of SSL VPN:
- Clientless Access: Users can access the VPN via a web browser without the need to install a software client.
- Granular Access Control: Allows for fine-tuned access to specific parts of a network.
- Cross-platform Compatibility: Can be accessed from any device with a web browser.
- Secure Connection: Uses SSL/TLS to encrypt the data ensuring that the data remains confidential and intact.
Question: What is the difference between IPSec and SSL VPN?
Answer: IPSec and SSL VPN are both protocols used to establish secure connections, but they differ in their applications, implementation, and mechanisms. Here's a comparison:
Connection Level:
- IPSec: Operates at the IP layer and secures all data that is sent from the source to the destination. It's often used for site-to-site VPNs.
- SSL VPN: Operates at the application layer and secures specific application sessions. It's commonly used for remote access.
Client Requirement:
- IPSec: Requires a specialized client software to establish a connection.
- SSL VPN: Typically does not require any special client software as it can be accessed through a web browser (clientless).
Granular Access:
- IPSec: Often provides access to the entire network.
- SSL VPN: Can provide fine-grained access to specific applications or sections of a network.
Ease of Use:
- IPSec: Configuration can be more complex due to its operating level and broader access.
- SSL VPN: Simpler to set up for remote access and is more user-friendly for end-users accessing via a browser.
Port Usage:
- IPSec: Uses specific ports, which might be blocked by some firewalls.
- SSL VPN: Uses standard SSL/TLS ports (e.g., port 443), which are usually open on most firewalls.
Question: What is the reason or where you would prefer NoSQL database over Relational Database?
Answer: NoSQL databases are preferred over Relational Databases (RDBMS) in certain situations due to their flexibility, scalability, and performance characteristics. Some reasons include:
- Scalability: NoSQL databases can horizontally scale out by adding more servers to the system, making them suitable for big data and high-velocity applications.
- Flexible Schema: NoSQL databases allow for flexible data models which can be easily modified without affecting existing data.
- Diverse Data Types: Ideal for semi-structured or unstructured data like JSON, XML, etc.
- Low Latency: Some NoSQL databases can provide low latency read and write operations which are useful for real-time applications.
- High Throughput: Suitable for applications that require massive read and write operations.
Question: Name five Linux commands which have 5 or more letters?
Answer:
- ‘mkdir’ (to create a directory)
- ‘rmdir’ (to remove a directory)
- ‘chmod’ (to change file permissions)
- ‘chown’ (to change file owner)
- ‘ifconfig’ (to configure a network interface)
Question: Can you describe a Web Application and all its components?
Answer: A web appl ication is a software program that runs on a web server and is accessed through a web browser over the Internet. Components include:
- User Interface: The frontend, including HTML, CSS, and JavaScript, which determines how the application looks and interacts with users.
- Application Logic: Backend code, written in languages like Python, Java, or PHP, that handles data processing, business logic, and interacts with databases.
- Database: Where data is stored, retrieved, and updated. Examples include MySQL, PostgreSQL, and MongoDB.
- Web Server: Software that serves web pages to users. Examples include Apache, Nginx, and IIS.
- Middleware: Software components that provide services to integrate different parts of the web application, such as authentication, session management, and caching.
- APIs: Interfaces that allow the web application to communicate with other services or applications.
- Hosting Environment: The infrastructure where the web application is hosted, such as cloud providers, dedicated servers, or shared hosting.
Question: Can you give a use case where you would use TCP and UDP?
Answer: TCP (Transmission Control Protocol): Ensures that all sent packets reach the destination in the correct order.
Use Case: File transfer where integrity and reliability are paramount, such as downloading a software update or accessing a website where the complete and ordered retrieval of all data is essential.
UDP (User Datagram Protocol): Sends packets without establishing a connection and does not guarantee packet delivery or order.
Use Case: Streaming services like online video or online gaming where real-time data transfer is more important than ensuring every single packet is received. If a few packets are lost in transit, it's more acceptable than introducing latency.
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