Distributed Systems Interview Questions and Answers

What is a distributed system? What are its advantages and disadvantages?

Answer: A distributed system is a system where multiple independent computers work together over a network to form a single system. Advantages include:
- High Availability: The system can continue working even if some parts fail.
- Scalability: The system can handle more load by adding more computers.
- Fault Tolerance: The system can handle certain types of errors and failures automatically.
Disadvantages include:
- Complexity: Designing and implementing the system is more complex due to network communication and data consistency issues.
- Network Latency: Communication over the network can introduce delays and affect performance.
- Data Consistency: Maintaining data consistency in a distributed environment is challenging.
How do you achieve data consistency in a distributed system?

Answer: Data consistency can be achieved through:
- Distributed Transactions: Using two-phase commit (2PC) or three-phase commit (3PC) protocols to ensure transaction consistency.
- Consistency Algorithms: Using algorithms like Paxos or Raft to ensure data consistency across multiple nodes.
- CAP Theorem: Balancing between Consistency, Availability, and Partition Tolerance based on the system’s requirements, choosing strong or eventual consistency models as needed.
What is the CAP theorem? How do you balance it in real systems?

Answer: The CAP theorem states that in a distributed system, it is impossible to achieve Consistency, Availability, and Partition Tolerance simultaneously. Definitions are:
- Consistency: All nodes see the same data at the same time.
- Availability: Every request receives a response, regardless of success or failure.
- Partition Tolerance: The system continues to work despite network partitions.
In real systems, you balance these based on the application needs. For example, financial systems may prioritize consistency, while social networks may prioritize availability.
What is idempotency? Why is it important in distributed systems?

Answer: Idempotency means that performing an operation multiple times has the same effect as performing it once. In distributed systems, due to unreliable networks, requests may be repeated. Ensuring operations are idempotent prevents side effects from repeated operations. For example, delete and update operations should be designed to be idempotent.
How do you design a highly available distributed system?

Answer: To design a highly available distributed system:
- Redundancy: Use replication and backups to ensure system components have redundancy.
- Fault Detection and Recovery: Implement automated fault detection and recovery mechanisms like health checks, auto-restart, and failover.
- Load Balancing: Use load balancers to evenly distribute requests across multiple servers to avoid single points of failure.
- Decentralization: Avoid single points of failure by using decentralized design.
What is microservices architecture? What are its pros and cons?

Answer: Microservices architecture splits an application into small, loosely coupled services, each independently deployable. Pros include:
- Independent Deployment: Each microservice can be deployed and updated independently without affecting others.
- Technology Diversity: Different microservices can use different tech stacks, choosing the best tool for each job.
- Scalability: Each microservice can be scaled independently based on its load requirements.
Cons include:
- Operational Complexity: Managing and monitoring multiple microservices is more complex.
- Network Overhead: Communication between microservices depends on the network, introducing latency and overhead.
- Data Consistency: Managing data consistency across services is more complex.

These questions and answers can help you demonstrate your knowledge and experience in distributed systems during an interview. I hope this helps!