What Is a System Design Interview?
A system design interview tests your ability to design large-scale distributed systems. You'll be asked to design something like a URL shortener, chat system, or news feed.
The 4-Part Framework
Every system design interview follows this structure:
1. Requirements (2-3 minutes)
Ask clarifying questions:
- How many users?
- What's the read/write ratio?
- What's the latency requirement?
- What's the availability target?
Don't skip this. Jumping into design without requirements is the #1 mistake.
2. High-Level Design (10 minutes)
Draw the major components:
- Client, load balancer, application servers, database
- Show the data flow with arrows
- Label everything clearly
- Keep it simple first
3. Deep Dive (15 minutes)
Pick ONE hard problem and go deep:
- Database schema and indexing
- Caching strategy
- Message queues for async processing
- Consistency vs availability trade-offs
4. Trade-offs (5 minutes)
Explain what you chose and why:
- SQL vs NoSQL
- Single leader vs multi-leader replication
- Strong consistency vs eventual consistency
5 Practice Problems
Start with these:
- URL Shortener - Hashing, redirects, analytics
- Chat System - Websockets, message storage, presence
- News Feed - Fan-out on write vs read, ranking
- Rate Limiter - Token bucket, sliding window
- Search Autocomplete - Trie data structure, ranking
Common Mistakes
- Not asking questions. Assumptions lead to wrong designs.
- Over-engineering. Start simple, optimize later.
- Ignoring trade-offs. Every decision has a cost.
- Running out of time. Practice under timed conditions.
Practice with ResumeSkool
We have 17 system design problems with detailed solutions. 4 are free to start.
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