# 07. Caching Strategy (Redis + HTTP Cache)

meta:
  id: web-production-07
  feature: web-production
  priority: P2
  depends_on: []
  tags: [performance, caching, production]

objective:
- Implement multi-layer caching to reduce database load and improve response times

deliverables:
- Redis caching layer for API responses
- HTTP cache headers for client-side caching
- Cache invalidation strategy
- Stale-while-revalidate pattern

steps:
1. Implement Redis caching for API responses:
   - Create web/src/server/lib/cache.ts with Redis-backed cache
   - Cache user profile: key `user:{id}`, TTL 5 minutes
   - Cache subscription: key `sub:{userId}`, TTL 1 minute
   - Cache dashboard summary: key `dash:{userId}`, TTL 30 seconds
   - Cache blog posts: key `blog:{slug}`, TTL 1 hour
2. Add cache decorators/procedures:
   - Create cachedProcedure wrapper for tRPC
   - Support cache tags for invalidation
3. Implement HTTP caching headers:
   - Static assets: Cache-Control: public, max-age=31536000, immutable
   - API responses: Cache-Control: private, max-age=30
   - HTML pages: Cache-Control: no-cache (SSR)
4. Add cache invalidation:
   - Invalidate user cache on profile update
   - Invalidate subscription cache on billing event
   - Invalidate blog cache on publish/edit
5. Implement stale-while-revalidate for dashboard data
6. Add cache hit/miss metrics

tests:
- Unit: Test cache set/get/delete operations
- Integration: Test cache invalidation on mutations
- Performance: Compare cached vs uncached response times

acceptance_criteria:
- Redis cache layer active on all read-heavy endpoints
- Cache hit rate >80% for user profile and subscription endpoints
- Cache invalidation working on all mutations
- HTTP cache headers correct per endpoint type
- Stale-while-revalidate pattern on dashboard widgets
- Cache metrics visible in monitoring dashboard

validation:
- Load test: cached endpoint p95 < 20ms
- Verify Redis keys created for cached data
- Update profile → cache invalidated, next request hits DB

notes:
- Redis already used for BullMQ jobs — share connection or use separate DB index
- Be careful caching authenticated data — always include userId in key
- Consider using Vercel KV or Upstash Redis for serverless