Avoiding repeated work.
WHERE CACHING HAPPENS
In the browser At a delivery network At a reverse proxy In the application In the database layer
WHAT TO CACHE
Expensive computations Repeated identical queries External responses that change rarely Static assets
WHAT NOT TO CACHE
Personal data, in a shared cache Anything that must always be current
WHAT THE HARD PROBLEM IS
Knowing when to invalidate.
WHAT TO DECIDE FOR EACH
How stale it may be What causes it to be cleared
WHAT TO USE FOR STATIC ASSETS
Long cache durations, with a version in the filename.
WHY
The content at a given address never changes, so it can be cached indefinitely, and a change produces a new address.
WHAT THAT SOLVES
Changes appearing immediately without disabling caching.
WHAT TO BE CAREFUL WITH
Caching authenticated responses Cache warming on deployment Cached errors
THAT LAST ONE
Caching a failed response serves the failure to everyone.
WHAT TO MEASURE
Hit rate, and whether it actually reduced load.
