Updated 2026-09-16
Backend engineer interviews focus on API design, data modelling, and operating services you own — not leetcode trivia alone. Expect questions on idempotency, database migrations under load, and how you debug a 500 spike at 2 am.
Product and platform teams hire backend engineers for reliability and clear contracts with frontend and mobile. Panels interview on transactional boundaries, observability, and whether you design for failure — retries, timeouts, dead letters.
Scenarios include hot keys in cache, migration rollback, and conflicting requirements from two product teams on the same endpoint.
Design a REST or event API for creating and canceling orders — key endpoints and idempotency.
Idempotency keys, clear states, cancel rules, conflict responses — not happy path only.
Walk me through a database migration you shipped with zero or minimal downtime.
Expand-contract or dual-write pattern, backfill plan, rollback — honest about complexity.
How do you debug elevated 500 errors when logs show many timeouts?
Trace downstream, pool exhaustion, deploy correlation, circuit breaker state — systematic.
Explain when you would use a queue versus synchronous call between services.
Latency tolerance, burst absorption, failure isolation — not queues everywhere.
What metrics and alerts do you add for a new production service?
Golden signals, SLO thought, alert on user impact not CPU alone — practical observability.
Use this as a starting point for structured interviews — not as a certified assessment. Adjust weights to match your company's standards and local labour norms.
| Criterion | What to listen for |
|---|---|
| API & data design | Idempotency; migration safety |
| Reliability | Timeouts, retries, failure modes |
| Operational ownership | On-call learning; useful metrics |
| Judgement | Sync vs async; service split skepticism |
Employers: screen this role at scale
Run the same structured questions across every applicant so hiring managers hear comparable answers before scheduling live interviews. See /hiring for how structured AI interviews fit bulk and frontline hiring.
Candidates: practise before the real interview
Answer these questions out loud — timing, clarity and examples matter more than memorising scripts. Use a mock interview to hear yourself under light pressure before the employer call.
Mid-level and above usually yes — junior may focus coding and SQL.
Posting language drives interview — polyglot teams may allow choice with justification.
Varies — know indexing and query plans; deep DBA may be separate role.
Some companies use bounded take-homes — ask time limit and evaluation criteria.
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Employers and candidates use the same question bank — structured screens for hiring teams, mock practice for applicants.