Part of series: System Design Roadmap
Week 8 Day 1: The Design Process - How to Ace Interviews
You walk into an interview. The interviewer says: “Design Twitter”. Panic? No. Follow the 4-Step Process.
Step 1: Clarify Requirements (5-10 mins)
Don’t start coding. Ask questions.
- Functional: “Can users post tweets? Retweet? Search?”
- Non-Functional: “How many DAU (Daily Active Users)? How fast must the feed load?”
- Math:
- 100M DAU.
- 10 tweets/user/day = 1B tweets/day.
- 1B * 1KB = 1TB Storage/day.
Step 2: High-Level Design (10-15 mins)
Draw boxes.
- “We need a Load Balancer.”
- “We need an App Server (Microservices: Tweet Svc, User Svc).”
- “We need a DB (SQL/NoSQL) and a Cache (Redis).”
- “We need Object Storage (S3) for images.”
Step 3: Deep Dive (15-20 mins)
Pick the hardest part and solve it.
- Twitter Feed: “How do we generate the home feed?”
- Pull Model (Slow) vs Push Model (Fan-out).
- Discuss Sharding strategy (User ID vs Tweet ID).
Step 4: Wrap Up (5 mins)
- Bottlenecks: “What if the Cache fails?”
- Monitoring: “We need Prometheus.”
- Scalability: “We can add more Read Replicas.”
Tomorrow: Applying this process to Twitter. 🐦