Interview guide
Backend Engineer interview questions
Backend interviews focus on API and data design, reliability, scaling and debugging distributed systems. Interviewers want to see you think about failure modes, not just the happy path.
Role-specific questions
1.How would you design an API for a booking system?
Why they ask: Resource modelling, consistency and edge cases.
How to answer: Model resources and states, idempotency for payments/bookings, how you prevent double-booking (transactions, locks or constraints), pagination and versioning.
2.When would you choose SQL vs a NoSQL database?
Why they ask: Trade-off thinking over hype.
How to answer: Relational for integrity and flexible queries; document/key-value for simple access patterns at huge scale. Tie it to a real decision you made.
3.A request is slow in production. How do you investigate?
Why they ask: Debugging method.
How to answer: Reproduce and measure: traces, logs, query plans. Narrow down (network, app, database), fix the bottleneck, add a guard or alert.
4.How do you handle a dependency that sometimes fails?
Why they ask: Resilience.
How to answer: Timeouts, retries with backoff and jitter, circuit breakers, graceful degradation, and idempotent operations so retries are safe.
5.How do you roll out a risky database migration?
Why they ask: Operational maturity.
How to answer: Expand–migrate–contract: add new structure, backfill, dual-write or switch reads, then remove the old path. Always have a rollback.
6.How do you keep services secure?
Why they ask: Security is everyone’s job on the backend.
How to answer: Least privilege, validate all input, parameterised queries, secrets management, dependency updates, and logging that helps without leaking data.
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Behavioral questions
Every backend engineer interview includes these. Answer with STAR: the Situation, your Task, the Actions you took, and the Result — with a number where you can.
7.Tell me about yourself.
Why they ask: It sets the frame for the whole interview and tests whether you can summarise your career around what they need.
How to answer: 90 seconds: present (current role and one proud result), past (the path that got you here), future (why this role is the logical next step). Skip your life story.
8.Tell me about a time you disagreed with a teammate or manager.
Why they ask: They want to see that you can push back with evidence and still commit once a decision is made.
How to answer: Use STAR. Show how you understood their view, what data you brought, how it was resolved — and what you did if you lost the argument.
9.Describe a project that failed or didn’t go to plan.
Why they ask: Ownership and learning matter more than a perfect track record.
How to answer: Pick a real failure you contributed to. Spend most of the answer on what you changed afterwards — ideally with a later result that proves it.
10.Tell me about a time you had to deliver under a tight deadline.
Why they ask: They’re testing prioritisation and communication, not heroics.
How to answer: Explain what you cut or re-scoped, who you told and when, and the outcome. Mention the trade-off you consciously accepted.
11.What’s an accomplishment you’re most proud of?
Why they ask: It shows what you value and the scale you operate at.
How to answer: Choose one relevant to this role. Make your personal contribution clear (“I”, not “we”) and end with a number.
12.Why do you want to work here?
Why they ask: They want evidence you chose them — not just any job.
How to answer: Connect something specific (their product, a recent launch, how the team works) to your experience and what you want to do next.