Cake Shop 2 - Scaling Up

How to Approach

Clarify requirements: Growing from 10k to 100k daily visitors. Same feature set but now peak traffic (3x) overwhelms a single server.

Estimate scale: 100k DAU / 86,400s ~= 1.2 RPS average. 3x peak ~= 3.5 RPS. A cache and a second API server are warranted.

Pick components:

• •Add Redis cache in front of PostgreSQL for product catalog reads (80%+ of traffic)
• •Add a load balancer to distribute across 2-3 API servers
• •Keep single PostgreSQL -- at this scale it handles writes fine
• •CDN still handles static assets

Key tradeoffs to discuss:

• •Cache invalidation: when a product price changes, how does the cache update? (TTL vs explicit invalidation)
• •Session storage: with multiple API servers, sessions must be stored in Redis (not in-memory)
• •Connection pooling: each API instance holds DB connections -- 3 instances x 20 connections = 60 total
• •Reads dominate writes (browsing >> purchasing), so a read cache has high impact