Top 73 System Design Interview Questions & Answers (2026)

01 What is system design? 02 What is scalability? 03 What is a load balancer? 04 What is caching and why is it important? 05 What is the CAP theorem? 06 What is a CDN (Content Delivery Network)? 07 What is the difference between SQL and NoSQL databases? 08 What is database sharding? 09 What is database replication? 10 What is a microservices architecture? 11 What is an API gateway? 12 What is consistent hashing? 13 What is the difference between REST and GraphQL? 14 What is eventual consistency? 15 What is a message queue and why is it used in system design? 16 What is a reverse proxy? 17 What is rate limiting? 18 What is the difference between synchronous and asynchronous communication in distributed systems? 19 What is a single point of failure (SPOF)? 20 What is high availability (HA)? 21 What is the difference between latency and throughput? 22 What is fault tolerance? 23 What is the difference between availability and reliability? 24 What is a distributed system? 25 What is idempotency and why is it important? 26 What is a circuit breaker pattern? 27 What are the ACID properties in databases? 28 What is the difference between horizontal and vertical scaling? 29 What is a content delivery network (CDN) and how does it reduce latency? 30 What is the difference between a monolithic and microservices architecture? 31 What is service discovery? 32 What is back-pressure in distributed systems? 33 What is the difference between push and pull architectures? 34 What are webhooks? 35 What is data partitioning? 36 What is a data lake vs a data warehouse? 37 What is event-driven architecture? 38 What is the difference between synchronous and asynchronous replication? 39 What is a blob store / object storage?

01 How would you design a URL shortener like bit.ly? 02 How would you design a rate limiter? 03 How would you design a Twitter/social media feed? 04 How would you design a distributed key-value store? 05 How would you design a notification system? 06 What is the CAP theorem and how does it apply to database choice? 07 What is event sourcing? 08 What is CQRS (Command Query Responsibility Segregation)? 09 What is the Saga pattern for distributed transactions? 10 What is a write-ahead log (WAL)? 11 How would you design a search engine like Elasticsearch? 12 What is the two-phase commit (2PC) protocol? 13 What is the Raft consensus algorithm? 14 How would you design a web crawler? 15 What is MapReduce and when would you use it? 16 What is a Bloom filter? 17 How would you design a ride-sharing app like Uber? 18 What is a time-series database and when should you use one? 19 What is the difference between message queues and event streaming platforms? 20 How would you design a chat application like WhatsApp?

01 How would you design a distributed file system like HDFS? 02 How would you design a video streaming service like Netflix? 03 What is the consistent hashing with virtual nodes in detail? 04 How would you design a global distributed database like Google Spanner? 05 What is the difference between optimistic and pessimistic locking in distributed systems? 06 How would you design Google's Bigtable? 07 What is the CAP theorem's extension — PACELC theorem? 08 How would you design a global distributed cache system? 09 What is a vector clock and how does it solve consistency problems? 10 How would you design an autocomplete / typeahead search system? 11 What is geo-sharding and how do you handle data locality requirements? 12 How would you design a distributed lock service? 13 What is zero-downtime deployment and how do you achieve it? 14 How would you design Instagram's system architecture?