Interview prep
Backend Developer interview questions
Backend interviews assess database design, API architecture, scalability, and reliability. Expect coding (SQL, patterns), system design for high load, and deployment considerations.
🎤 Practice these out loud with AceCoach →The questions
Design a notification system that delivers 1M notifications/minute with guaranteed delivery. System design
How to answerQueue-based buffering (Kafka/RabbitMQ), idempotency, multi-channel (push/email/SMS), retry with exponential backoff, monitoring.
Write SQL to find users who bought item A but never item B, ordered by last purchase date desc. Coding
How to answerNOT EXISTS or LEFT JOIN … IS NULL with date filtering; index user_id and item; test NULL dates.
A query that ran in 1s now takes 8s. Debug and fix. Scenario
How to answerEXPLAIN plan; look for full scans (missing index), bad join order, Cartesian products, or schema change; add indexes or refactor.
Tell me about a production outage you debugged that affected thousands of users. Behavioral
How to answerSTAR: service + impact, detection/alerting, root cause via logs/metrics + mitigation, recovery time and prevention.
Explain indexing strategies. When composite vs separate indexes? Fundamentals
How to answerB-tree for ranges, hash for equality; composite for multi-column WHERE/JOIN; cost is write amplification and storage.
Design a rate limiter of 100 req/min per user across multiple servers. System design
How to answerToken bucket or sliding window with distributed state (Redis), atomic increments, TTL keys, return 429 + retry-after.
What backend developers are tested on
Node.js/Python/JavaSQL/NoSQL DatabasesREST/GraphQL APIsScalability & CachingMessage QueuesDocker/KubernetesMicroservicesSecurity & Authentication
Frameworks are guidance, not scripts — the point is to make the answers your own. All roles →