4 lessons
What caching actually is
Trading a little staleness for a lot of speed, and the memory hierarchy idea underneath every cache in a computer system.
Cache invalidation and the standard caching patterns
The genuinely hard problem in caching: knowing when a cached answer has gone stale, and the standard patterns for handling it.
Redis and in-memory data stores
The technology most caches are actually built on, what makes it so fast, and the other jobs it ends up doing beyond caching.
CDNs and caching close to the user
Caching applied to physical distance itself — why a static file should be served from near the user, not from your one origin server.