System Design & Software Architecture Questions Interview Questions and Answers

System Design & Software Architecture Questions Interview Questions and Answers

Practice one question at a time. Read the question, answer aloud, then compare your explanation with the answer.

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Study method: define the concept, give a small example, and mention one practical use or limitation.

Q1. What is System Design and why is it crucial for software engineering?

Easy

Answer: System design is the process of defining the architecture, modules, interfaces, and data strategy for a system to satisfy specific functional and non-functional requirements (such as availability, scalability, latency, reliability, and security).

Interview tip: Use a short example and connect the answer to real project work.

Q2. What is Horizontal vs Vertical Scaling?

Easy

Answer: Vertical scaling (Scale Up) adds more power (CPU, RAM, Storage) to a single machine, but has hardware limits and single point of failure risk. Horizontal scaling (Scale Out) adds more machines to the pool, distributing load across servers using a Load Balancer for elastic scaling.

Interview tip: Use a short example and connect the answer to real project work.

Q3. What is a Load Balancer and what algorithms does it use?

Easy

Answer: A load balancer distributes incoming network traffic across multiple backend servers to prevent overload and ensure high availability. Popular algorithms include Round Robin, Least Connections, IP Hash, and Weighted Round Robin.

Interview tip: Use a short example and connect the answer to real project work.

Q4. Explain Caching Strategies (Redis/Memcached) and Cache Invalidations.

Medium

Answer: Caching stores frequently accessed data in fast in-memory stores like Redis or Memcached to reduce database load and lower response latency. Common caching strategies include Cache-Aside (Lazy Loading), Write-Through, Write-Behind, and Read-Through. Cache eviction algorithms include LRU (Least Recently Used) and LFU.

Interview tip: Use a short example and connect the answer to real project work.

Q5. What is Database Sharding vs Replication?

Medium

Answer: Database Replication copies data across multiple nodes (Primary/Leader handles writes, Replicas handle reads) to increase read throughput and failover redundancy. Database Sharding horizontally partitions a large database into smaller independent shards based on a Shard Key (e.g., user_id % N) to distribute write load.

Interview tip: Use a short example and connect the answer to real project work.

Q6. Explain the CAP Theorem in Distributed Systems.

Medium

Answer: CAP theorem states that a distributed system can simultaneously guarantee at most two out of three guarantees: Consistency (every read gets the most recent write), Availability (every non-failing node returns a response), and Partition Tolerance (system functions despite network drops). Systems choose CP (e.g., HBase, MongoDB) or AP (e.g., Cassandra, DynamoDB).

Interview tip: Use a short example and connect the answer to real project work.

Q7. How do Message Queues (Kafka, RabbitMQ) work in Event-Driven Architecture?

Hard

Answer: Message queues decouple service communication. Producers publish events/messages to topics or queues, and Consumers process them asynchronously. Apache Kafka uses a distributed, append-only log model for high-throughput streaming, while RabbitMQ uses an exchange and queue routing model for reliable messaging.

Interview tip: Use a short example and connect the answer to real project work.

Q8. How would you design a URL Shortener service like Bit.ly?

Hard

Answer: Key components include: 1) API Gateway for HTTP requests, 2) Base62 encoding algorithm to convert auto-increment IDs or MD5 hashes into short 7-character strings, 3) NoSQL/Key-Value DB (DynamoDB/Cassandra) for fast mapping storage, 4) Redis Cache for popular short URLs, 5) 301 Permanent Redirect for SEO or 302 Temporary Redirect for analytics tracking.

Interview tip: Use a short example and connect the answer to real project work.

Quick revision checklist

1. Explain the answer without reading.
2. Write one small example.
3. Review platform or version differences in official documentation.