The System Design Interview Framework
System design questions test your ability to think at scale. The interviewer wants to see your thought process, not a perfect answer. Here's a reliable framework.Step 1: Clarify Requirements (2-3 minutes)
Never jump into design. Ask:- Functional requirements: What should the system do?
- Non-functional requirements: Scale, latency, availability?
- Constraints: Read-heavy or write-heavy? Geographic distribution?
Example for URL Shortener: "So we need to generate short URLs, redirect quickly, and handle maybe 1000 writes/sec and 10x that in reads. Should we support custom aliases? Analytics?"
Step 2: High-Level Design (5-8 minutes)
Draw the main components and how they connect:- API Gateway — entry point
- Application servers — business logic
- Database — storage
- Cache — performance
- CDN — static content
- Message queue — async processing
Example: "At a high level, I'd have an API service that takes a long URL, generates a base62 hash from a counter or snowflake ID, stores the mapping in a key-value store like DynamoDB, and returns the short URL. For reads, it's just a lookup and 301 redirect."
Step 3: Deep Dive (10-15 minutes)
Pick 2-3 critical areas and go deep:Database Choice
- SQL (PostgreSQL) — when you need ACID, complex queries, relationships
- NoSQL (DynamoDB, Cassandra) — when you need scale, simple lookups, high write throughput
- Redis — caching, session storage, rate limiting
Scaling Strategy
- Horizontal scaling — add more servers behind a load balancer
- Database sharding — partition data across multiple DB instances
- Caching — reduce DB load (Redis, CDN)
- Async processing — queues for non-critical paths
Trade-offs
Always mention trade-offs. Interviewers love this:- "The downside with eventual consistency is [X], but for our use case it works because [Y]"
- "We could use a relational DB for stronger consistency, but at this scale NoSQL gives us [Z]"
Step 4: Address Edge Cases (2-3 minutes)
- What happens if a server goes down?
- How do you handle duplicate requests?
- What about rate limiting / abuse?
- Monitoring and alerting?
Common System Design Questions
- Design a URL shortener — hashing, key-value store, redirect caching
- Design a chat system — WebSockets, message queues, presence
- Design Twitter/Instagram feed — fan-out, timeline generation, caching
- Design a rate limiter — sliding window, token bucket, distributed state
- Design a notification system — push, email, SMS, priority queues
How TryCuebird Helps with System Design
During live system design interviews, TryCuebird can:- Listen to the question and generate a structured starting point
- Analyze screen-shared diagrams and suggest improvements
- Provide specific technology choices with trade-offs
- Keep your answer organized when nerves take over
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