Architecture under constraints
System Design Interview Questions
Scalability, consistency, queues, storage and trade-off reasoning for mid-level and senior system design rounds.
40 questions10 easy22 medium8 hard0/40 learned
01How do you structure a system design interview answer?Easyinterview framework · requirements · tradeoffs02What is the difference between functional and non-functional requirements?Easyrequirements · non-functional · constraints03What is the difference between latency and throughput?Easylatency · throughput · performance04What does scalability mean in system design?Easyscalability · bottlenecks · growth05How does load balancing work and how do you choose an algorithm?Mediumload balancing · l4 · l706How do you scale an application horizontally?Easyhorizontal scaling · stateless · sessions07What caching layers and patterns should you know?Easycaching · invalidation · cache patterns08How does a CDN work and when should you use one?Easycdn · edge caching · cache control09How does database sharding work and what are the pitfalls?Mediumsharding · partitioning · hotspots10How does database replication work and what consistency issues does it create?Mediumreplication · replication lag · failover11What does the CAP theorem actually say?Mediumcap theorem · consistency · availability12What consistency models should you know and when do they matter?Hardconsistency models · linearizability · session guarantees13How do ACID and BASE differ, and is one always better?Easyacid · base · transactions14How do you choose between SQL and NoSQL in a system design?Mediumsql · nosql · access patterns15What problems do message queues solve and what guarantees do they provide?Mediummessage queues · delivery semantics · backpressure16How does publish-subscribe differ from a message queue?Mediumpub-sub · fan-out · consumer groups17What is event-driven architecture and what are its failure modes?Mediumevent-driven · events · eventual consistency18What does an API gateway do and what risks does it introduce?Mediumapi gateway · routing · cross-cutting19When should you choose microservices over a monolith?Easymicroservices · monolith · service boundaries20How does service discovery work in a dynamic environment?Mediumservice discovery · registry · health checks21How would you design rate limiting across a distributed service?Mediumrate limiting · token bucket · distributed counters22How do idempotency and retries work together?Mediumidempotency · retries · exactly-once23How do distributed transactions work and why are they hard?Harddistributed transactions · two-phase commit · consistency24How does the saga pattern handle long-running business transactions?Hardsaga · compensation · orchestration25What is the transactional outbox pattern and why is it needed?Hardoutbox · dual write · change data capture26How do distributed locks work and when are they unsafe?Harddistributed locking · fencing tokens · leases27How does consistent hashing work and why is it useful?Mediumconsistent hashing · virtual nodes · partitioning28How would you design a URL shortener?Mediumurl shortener · key generation · caching29Design a rate limiter for a public API.Mediumrate limiter · token bucket · redis30How would you design a chat system?Mediumchat · websockets · message ordering31How would you design a news feed?Mediumnews feed · fan-out · ranking32How would you design a file storage service?Hardfile storage · object storage · presigned urls33How would you design search autocomplete?Mediumautocomplete · trie · top-k34How would you design a notification system?Mediumnotifications · fan-out · delivery tracking35How would you design a payment system?Hardpayments · ledger · idempotency36What makes a system observable?Mediumobservability · metrics · tracing37What are SLIs, SLOs and SLAs, and how do error budgets work?Easysli · slo · error budget38How do you plan disaster recovery with RTO and RPO?Harddisaster recovery · rto · rpo39How do you estimate capacity for a system design?Mediumcapacity planning · estimation · back of envelope40How do you communicate design trade-offs in an interview?Mediumtradeoffs · communication · decision making
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