http cache: keeping it fresh

Keeping it fresh David de Boer

Hello

• I’m David

• Lead developer at Driebit, Amsterdam

• Open source fanatic

The problem

• E-learning platform

• Now used by ~50% of Dutch primary and secondary schools

• Slow

So cache!

• Keep coding fun

• Keep users happy

Caching models

!

• Expiration

• Validation

• Invalidation

What we had

• REST API

• Content changes at predictable moments

• Rush hour

What we needed

• Fresh data at push of button

• Talk to Symfony as little as possible

Back to caching modelsQuick

refreshDon’t talk

to Symfony

Expiration × ✔

Validation ✔ ×

Invalidation ✔ ✔

– Phil Karlton

“There are only two hard things in Computer Science: cache invalidation and naming things.”

– Symfony2 documentation

“You should never need to invalidate cached data…”

“Actually, all reverse proxies provide ways to purge cached data, but you should avoid them as much as possible.”

Varnishsub  vcl_hit  {    if  (req.request  ==  "PURGE")  {        purge;        error  200  “Purged";    }}

• Easy to use

• Configure, don’t code

• Lightweight

Easy to use

• Copy original route parameters

• Note: don’t use getRouteCollection()!

• $cacheManager    -­‐>invalidateRoute('my_route')    -­‐>flush();

Configure, don’t codedriebit_http_cache:    http_cache:        varnish:            ips:  [127.0.0.1,  123.123.123.1]            host:  yourapp.nl  

   invalidators:        exam_create:            origin_routes:  [  exams_post  ]            invalidate_routes:                exam_get_collection:  ~  #  /exams        exam_change:            origin_routes:  [  exam_put,  exam_del  ]            invalidate_routes:     exam_get_collection:  ~    #  /exams                exam_get:  ~                          #  /exams/{id}                current_exam:  ~                  #  /exams/current

Lightweight

• Collect all routes that will be invalidated.

• Send PURGE requests in kernel.terminate.

• Send them in parallel.

Christmas wish list

• Cache tags (X-­‐Id:  123)

• Annotations (Expression Language)

• Message queues

Thanks!• david@driebit.nl / @ddeboer_nl

• driebit/http-cache-bundle

• https://github.com/driebit

• https://github.com/ddeboer

• http://driebit.nl