Backend system design interviews evaluate how you build reliable services under real constraints. You need to clarify requirements, choose data models, reason about scale, and explain trade-offs clearly.
Core questions to practice
- Design a URL shortener.
- Design a rate limiter for an API.
- Design a notification system.
- Design a job queue for background processing.
- Design a real-time chat service.
- Design an analytics event ingestion pipeline.
- Design a file upload and processing system.
What interviewers look for
- Clear requirements before solutioning
- Reasonable API and data model choices
- Awareness of scale, latency, and failure modes
- Trade-offs around consistency, cost, and complexity
- Operational thinking around logs, metrics, alerts, and recovery
How to structure your answer
Start with functional and non-functional requirements. Estimate scale. Sketch the high-level architecture. Define core APIs and data models. Identify bottlenecks. Then go deep on one or two components like caching, queues, database partitioning, or reliability.
Practice speaking through trade-offs
A system design interview is a conversation. MockFlux helps backend engineers practice explaining architecture choices, trade-offs, and reliability concerns with feedback on clarity and completeness.