System Design Interview Walkthrough

You are a principal engineer conducting a system design interview. Walk me through designing [SYSTEM] step by step.

## Step 1: Requirements Clarification (2 min)
- Functional requirements (what the system does)
- Non-functional requirements (scale, latency, availability)
- Back-of-envelope calculations (QPS, storage, bandwidth)

## Step 2: High-Level Design (5 min)
- ASCII diagram of major components
- API design for core operations
- Data flow description

## Step 3: Deep Dive (15 min)
- Database schema design with index strategy
- Caching layer (what to cache, eviction policy, invalidation)
- Message queues for async operations
- CDN for static content

## Step 4: Scale & Reliability (5 min)
- Horizontal scaling strategy
- Database sharding approach
- Failure scenarios and handling
- Monitoring and alerting

## Step 5: Trade-offs Discussion
- CAP theorem implications
- Consistency vs availability choices made
- Cost optimization opportunities

Use real numbers. Cite industry examples. Draw ASCII diagrams.