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Backend Engineer interview questions
This interview focuses on your ability to design, build, and debug large-scale backend systems. Expect deep dives into distributed systems, databases, caching, APIs, observability, and security.
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backend engineer interview questions
Candidates preparing for a Backend Engineer interview who want real, topic-organized questions and how to prepare.
Distributed Systems interview questions
This section tests your ability to design scalable, fault-tolerant systems. Interviewers want to see your reasoning on trade-offs like consistency vs. availability.
- Design a URL shortener that serves 1B reads/day with sub-50ms p95. Cover write path, ID generation, hot-key mitigation.
- Walk through how you'd implement a rate limiter that scales horizontally across N API servers. Tradeoffs of token bucket vs leaky bucket vs sliding window.
- Design an async job queue with at-least-once semantics. Cover visibility timeout, dead letters, idempotency keys.
- You're seeing tail latency spikes every 10 minutes. Walk through your debugging steps before you blame GC.
Databases interview questions
These questions probe your understanding of database internals and performance. They assess how you choose indexing, locking, and partitioning strategies for real-world workloads.
- When does adding an index hurt instead of help? Give 2 concrete cases.
- Walk through the trade-offs between optimistic and pessimistic locking for a high-write counter.
- Explain how Postgres handles MVCC. What's the cost when transactions are long-running?
- You have a 10TB events table queried by user_id + date. Pick a partitioning strategy and defend it.
Caching interview questions
This section evaluates your caching strategy and ability to prevent performance degradation. Interviewers look for practical knowledge of invalidation and stampede mitigation.
- When would you reach for Redis vs an in-memory LRU vs Postgres? Concrete example for each.
- Walk through cache invalidation strategies for a multi-region read-heavy app. What's hardest about each?
- You have a thundering herd on cache miss. Three strategies — pick one and defend it.
- Explain cache stampede. How does request coalescing help?
API Design interview questions
These questions assess your API design philosophy and ability to handle integration complexity. They probe your experience with protocols, versioning, and long-running operations.
- When would you reach for GraphQL vs REST vs gRPC? Concrete project + reasoning.
- Walk through how you'd version an API that has 500 active third-party integrations.
- Explain idempotency keys. Where have you seen them implemented poorly?
- Design an API for a long-running export (10 minutes to compute). What's the contract with the client?
Observability interview questions
This section tests your operational maturity and debugging methodology. Interviewers want to see how you systematically diagnose issues using metrics, logs, and traces.
- You're paged at 3am for "API latency high." Walk through your first 10 minutes.
- Explain the difference between metrics, logs, and traces. When have you needed all three to debug something?
- What's the most useful dashboard you've built? Why?
- When do you reach for distributed tracing vs structured logs? Where do they overlap?
Security interview questions
These questions evaluate your security mindset and ability to protect systems. They probe your understanding of authentication, authorization, and incident response.
- Walk through how OAuth 2.0 authorization code with PKCE works. Why is PKCE there?
- Explain JWT vs session tokens. When would you actually choose JWT?
- You discover a SQL injection in a 5-year-old endpoint. Triage steps before pushing the fix.
- Walk through how you'd secure an internal admin API. What auth, what audit, what blast-radius limits?
Fast answers
What questions are asked in a Backend Engineer interview?
Backend Engineer interviews focus on areas like Distributed Systems, Databases, Caching, API Design. This page lists 24 real, scenario-based questions across those topics. JobFitPack can tailor practice to the specific role and resume you are targeting.
How should I prepare for a Backend Engineer interview?
Prepare concrete examples for each topic rather than memorizing definitions. JobFitPack turns a target job description and your resume into the likely questions and the gaps to rehearse.
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