But... why?

• Response time
• Scale with load
• Save resources and money

HTTP: Your browser chats with the webserver

Request

Response

HTTP verbs

• GET
• HEAD
• POST
• PUT
• DELETE
• ...

HTTP response codes

• 1xx hold on
• 2xx here you go
• 3xx go away
• 4xx you fucked up
• 5xx I fucked up

twitter.com/stevelosh/status/372740571749572610

HTTP Cache Control

Cache control headers

• Cache Expiration Model
• Cache Validation Model

HTTP 1.1, RFC 2616, Sections 13.2 and 13.3

Cache Expiration

• s-maxage
• max-age
• Expires (HTTP 1.0 - avoid!)

Cache validation

• Application specific hash value on response
• On request, cheap check if hash changed

ETag: 82901821233

If-None-Match: 82901821233

304 Not Modified

Do not cache

• s-maxage=0: Do not keep in cache
• private: For specific user, do not cache on proxies
• no-cache: Needs to be validated each time
• no-store: May never be placed in cache storage

Keep variants apart

Response content depends on request headers

Requests

Response

Cache busting

• Very long cache lifetime for assets
• Append ?version to asset links
• Query string to miss the cache

CDN / Reverse Proxy

Control your reverse proxy

Check documentation of your surrogate!