System design rounds can assess how you reason about requirements, scale and trade-offs. Practising explanations aloud helps you prepare beyond memorising an architecture. This guide offers a reusable framework and practice prompts, not a measured ranking of interview questions.
A framework that works for any question
Whatever the prompt, walk through these steps out loud. Interviewers reward structure far more than a "perfect" answer.
- Clarify requirements — functional ("users can shorten a URL") and non-functional ("100M reads/day, low latency"). Never start drawing boxes immediately.
- Estimate scale — back-of-envelope QPS, storage, and read:write ratio. This drives every later decision.
- Define the API — the handful of endpoints the system exposes.
- High-level design — client, load balancer, app servers, database, cache, queue. Draw the happy path.
- Deep-dive a component — pick the hardest part (the data model, the cache strategy, the bottleneck) and go deep.
- Discuss trade-offs — consistency vs availability, SQL vs NoSQL, sharding, replication, failure handling.
System design practice questions
Classic design problems
- Design a URL shortener (TinyURL) — tests hashing, key generation, read-heavy caching.
- Design a rate limiter — token bucket vs sliding window, where it lives.
- Design a news feed (Instagram/Twitter) — fan-out on write vs read, ranking.
- Design a chat system (WhatsApp) — websockets, delivery receipts, message storage.
- Design a ride-hailing service (Uber/Ola) — geospatial indexing, matching, surge.
- Design a video streaming service (YouTube/Hotstar) — CDN, encoding, storage tiers.
Infrastructure & scale questions
- How would you scale a read-heavy service to 10M users?
- How do you keep a cache consistent with the database?
- How do you design for high availability across regions?
- When would you choose NoSQL over a relational database?
- How do you handle a thundering-herd / hot-key problem?
India-specific signals to weave in
Where relevant to the prompt, consider peak-load events such as sales or festivals, UPI/payment idempotency, and mobile-first, low-bandwidth constraints. Explain why each matters to the design rather than assuming a particular employer expects it.
How to actually get good at this
System design is a spoken skill. You cannot learn it only by reading — you have to practise articulating a design under time pressure. Study the patterns, then rehearse explaining them aloud until the framework is automatic.
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A LITTLE MORE CLARITY
Frequently asked questions
How do I start a system design interview?
Always start by clarifying functional and non-functional requirements, then estimate scale (QPS, storage, read:write ratio). Jumping straight to drawing the architecture is the most common mistake.
What do interviewers actually look for?
Structured reasoning and trade-off awareness — not a single "correct" architecture. They want to see you handle ambiguity, justify decisions, and identify bottlenecks.
How long should I prepare for system design?
Preparation time depends on your experience and the role. Practise explaining designs aloud, identify weak areas through feedback, and revisit the trade-offs. No fixed number of weeks guarantees readiness or an interview outcome.