You now understand caching.
Caching reduces latency from ms to ms by storing data in memory.
Strategies: Cache-Aside (most common), Write-Through, Write-Behind, Refresh-Ahead.
Eviction: LRU is the default. Use TTL as a secondary mechanism.
Invalidation is hard. TTL is simple. Events are accurate but complex.
Redis is the default distributed cache. Use Memcached for simple key-value.
CDNs cache static content at the edge. Use for images, videos, CSS.
Prevent cache stampedes with locking or jittered TTL.