Backend Developer Interview
Questions & Answers

Stateless design so any instance can handle any request. Rate limiting and authentication at the API gateway layer. Pagination on all list endpoints. Async processing for long-running operations (queue + webhook callback). Caching at multiple layers (CDN, application, database). The key is designing for horizontal scaling from day one — no server-side session state.

Parameterised queries / prepared statements — never concatenate user input into SQL strings. Use an ORM with query builder that handles parameterisation automatically. Input validation as defence-in-depth, not primary protection. Principle of least privilege for database users — your app user should not have DROP or schema-altering permissions. Audit queries in code review for raw string concatenation.

Start with the access patterns: what queries will run most frequently, at what volume, with what filters. Schema follows query patterns, not object models. Define indexes on columns used in WHERE, JOIN, and ORDER BY. Consider write vs read ratio — heavy read workloads may need denormalisation or read replicas. Document constraints and foreign keys — rely on the database to enforce data integrity.

Take a heap snapshot before and after load, compare retained objects. Look for growing closures, EventEmitter listeners not removed, or caches without eviction policies. Use --inspect flag and Chrome DevTools for live heap profiling. In production, monitor memory with a time-series metric — a sawtooth pattern (grows then drops on restart) is the classic leak signature.

URL path versioning (/v1/, /v2/) is the most explicit and easiest to document. Header versioning is cleaner but harder for consumers to debug. Never make breaking changes within a version. Deprecation cycle: announce the old version end-of-life date at least 6 months before, return a Deprecation header on old-version responses, and monitor traffic before switching off.

Structure your answer as a 60-second professional narrative: where you have been (your background), what you have done (your strongest achievement), and where you are going (why this role). Lead with your most relevant experience, not your entire career history. End with why you are excited about this specific opportunity.

Choose a genuine weakness that you have actively worked to improve. The structure is: name the weakness → show self-awareness of its impact → describe the concrete step you took to address it → show the improvement. Never say "I work too hard" — interviewers recognise this as evasion and it damages your credibility.

Use the STAR method (Situation, Task, Action, Result) but add a fifth element: what you learned. Choose a real failure, not a disguised success. Show you can take responsibility without making excuses, and demonstrate that the lesson changed your behaviour in a specific, verifiable way.

Be honest but constructive. Acceptable reasons: seeking greater scope, new challenge, skills you can not develop in the current role, or company-level changes (restructuring, direction shift). Never speak negatively about your current employer or manager — it signals you will do the same to the prospective employer in future conversations.

Describe the conflict specifically, show that you sought to understand the other person's perspective, and explain the resolution approach you took. Interviewers are assessing your emotional intelligence and whether you escalate or resolve. Avoid stories where you were right and they were wrong — choose a story where both parties grew.

Describe your specific prioritisation system: impact × urgency matrix, stakeholder alignment, or a specific tool or process you use. Then give an example where you applied it under real pressure. Show that your system is systematic rather than reactive, and that you communicate proactively when priorities change.

Choose an achievement that is specific, measurable, and relevant to the role. Lead with the result ("I reduced our error rate by 40% in 90 days"), then explain the context, challenge, and what you specifically did that drove the result. Show your ownership and impact, not just your team's work.

Be honest about your ambitions while showing that this role is a genuine step in that direction — not a stopgap. Hiring managers want to invest in people who will grow with the organisation. Show that your 5-year goal requires the specific skills and experience this role provides, making your ambition an asset for both sides.

Research before the interview and make the answer specific: cite their product, a recent company development, something about their culture or team, or a professional aspect of this particular role that matches your goals. Generic answers ("I love your values") signal you did not do the research. Specific answers signal genuine interest.

Always have 3–5 questions prepared. Ask about the biggest challenge in this role, what success looks like in the first 90 days, how the team operates, and the interviewer's own experience at the company. Never ask about salary, benefits, or holidays in a first interview. Questions show interest, strategic thinking, and that you care enough to have done research.