Caching the Uncacheable
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This document provides an overview of using caching to serve visitor-specific content quickly while avoiding server-side sessions. It discusses using HTTP caching headers, a reverse proxy like Varnish, and the Symfony cache to cache responses varying by target groups identified in request cookies. The target groups are reevaluated on cache hits by making conditional requests in the reverse proxy layer using Varnish configuration.
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Caching the Uncacheable
- 1. Or how to make visitor specific content super fast. Caching the uncachable
- 2. I'm Daniel Rotter @danrot90 | https://github.com/danrot core developer and support guru. Passionate traveler and soccer player.
- 3. Who knows about HTTP Caching?
- 4. HTTP Caching Basics A short recap
- 5. Browser Reverse Proxy Symfony Application GET / GET / 200 OK 200 OK Browser GET / 200 OK
- 6. GET / HTTP/1.1 200 OK Cache-Control: public, max-age=3600, s-maxage=86400 <!DOCTYPE html> <html> <body> Interesting content </body> </html>
- 7. GET / HTTP/1.1 200 OK Last-Modified: Sun, 4, Feb 2018 20:18:00 GMT <!DOCTYPE html> <html> <body> Quite recent Content </body> </html> GET / If-Modified-Since: Sun, 4 Feb 2018 20:18:00 GMT HTTP/1.1 304 Not Modified
- 8. Apply more logic in the reverse proxy layer Custom HTTP Header
- 9. 200 OK Cache-Control: max-age=240 Browser Reverse Proxy Symfony Application GET / GET / 200 OK Cache-Control: max-age=240 200 OK X-Reverse-Proxy-TTL: 2400 Browser GET /
- 10. 200 OK Cache-Control: max-age=240 200 OK X-Reverse-Proxy-TTL: 2400 200 OK Cache-Control: max-age=240 Browser Reverse Proxy Symfony Application GET / GET / Browser GET / PURGE / GET / 200 OK X-Reverse-Proxy-TTL: 2400
- 11. Caching Implementations Symfony Cache or Varnish?
- 12. Symfony Cache – Easy to setup – Implemented in PHP – Not feature complete
- 13. // src/CacheKernel.php <?php namespace App; use SymfonyBundleFrameworkBundleHttpCacheHttpCache; class CacheKernel extends HttpCache {} // public/index.php <?php use AppKernel; use AppCacheKernel; // ... $kernel = new Kernel($env, $debug); $kernel = new CacheKernel($kernel); // ...
- 14. // src/Controller/NameController.php <?php namespace AppController; use SymfonyComponentHttpFoundationResponse; use SymfonyComponentRoutingAnnotationRoute; class NameController { /** * @Route("/name/{name}") */ public function index(string $name) { $response = new Response('Your name is ' . $name); $response->setSharedMaxAge(3600); return $response; } }
- 15. – Harder to setup – Implemented in C – Super performant – Many more features – Configured using VCL Varnish
- 16. Varnish Installation 1. Actually install varnish 2. Start varnish on port 80 3. Start your application on a different port 4. Tell varnish on which port your application is running 5. Add varnish as a trusted proxy in Symfony 6. Add cache headers to your responses 7. Configure the cache with VCL in more detail
- 17. # default.vcl vcl 4.0; # Default backend definition. Set this to point to your content server. backend default { .host = "127.0.0.1"; .port = "8080"; } 4
- 18. // public/index.php // ... Request::setTrustedProxies(['127.0.0.1'], Request::HEADER_X_FORWARDED_ALL); // ... 5
- 19. // src/Controller/NameController.php <?php namespace AppController; use SymfonyComponentHttpFoundationResponse; use SymfonyComponentRoutingAnnotationRoute; class NameController { /** * @Route("/name/{name}") */ public function index(string $name) { $response = new Response('Your name is ' . $name); $response->setSharedMaxAge(3600); return $response; } } 6
- 20. # default.vcl sub vcl_recv { # Happens before we check if we have this in cache already. # # Typically you clean up the request here, removing cookies you don't need, # rewriting the request, etc. } sub vcl_deliver { # Happens when we have all the pieces we need, and are about to send the # response to the client. # # You can do accounting or modifying the final object here. } 7
- 22. Audience Targeting Show (and cache!) different content for different target groups on the same URL
- 23. Audience Targeting Goals – Differentiate between different visitor target groups – Target groups are evaluated by a ruleset – first visit – each browser session – each hit – Do not start a session on the server – Cache the response per target group
- 27. Who knows the Vary header?
- 28. Browser Reverse Proxy Symfony Application GET /en Accept-Encoding: gzip 200 OK Vary: Accept-Encoding GET /en Accept-Encoding: identity 200 OK Cache-Control: max-age=0 GET /en Accept-Encoding: gzip 200 OK Vary: Accept-Encoding GET /en Accept-Encoding: gzip 200 OK Vary: Accept-Encoding Browser 200 OK Vary: Accept-Encoding GET /en Accept-Encoding: identity
- 29. Browser Reverse Proxy Symfony Application GET /en GET /_sulu_target_group X-Sulu-Original-Url: /en GET /en X-Sulu-Target-Group: 1 200 OK X-Sulu-Target-Group: 1 200 OK Vary: X-Sulu-Target-Group X-Reverse-Proxy-TTL: 2400 200 OK Cache-Control: max-age=0 Set-Cookie: _svtg=1; Set-Cookie: _svs=...; GET /en Cookie: _svtg=1; _svs=.. 200 OK Cache-Control: max-age=0
- 30. Reverse Proxy Symfony Application GET /about-us Cookie: _svtg=1; _svs=.. GET /about-us X-Sulu-Target-Group: 1 200 OK X-Reverse-Proxy-TTL: 2400200 OK Browser Browser GET /about-us Cookie: _svtg=1; _svs=.. 200 OK
- 31. Symfony Cache Use extended version of the SymfonyCache from Sulu to support Audience Targeting
- 32. <?php namespace SuluComponentHttpCache; use SymfonyBundleFrameworkBundleHttpCacheHttpCache as AbstractHttpCache; use SymfonyComponentHttpKernelHttpKernelInterface; class HttpCache extends AbstractHttpCache { public function __construct(HttpKernelInterface $kernel, $hasAudienceTargeting = false, $cacheDir = null) { parent::__construct($kernel, $cacheDir); $this->hasAudienceTargeting = $hasAudienceTargeting; } }
- 33. // app/WebsiteCache.php <?php use SuluComponentHttpCacheHttpCache; class WebsiteCache extends HttpCache { }
- 34. // web/website.php <?php // ... $kernel = new WebsiteKernel(SYMFONY_ENV, SYMFONY_DEBUG); $kernel->loadClassCache(); if (SYMFONY_ENV != 'dev') { $kernel = new WebsiteCache($kernel, true); Request::enableHttpMethodParameterOverride(); } // ...
- 35. Varnish VCL to the rescue!
- 36. “I really love VCL! Said no one, ever.
- 38. vcl 4.0; import header; backend default { .host = "127.0.0.1"; .port = "8000"; } sub vcl_recv { if (req.http.Cookie ~ "_svtg" && req.http.Cookie ~ "_svs") { set req.http.X-Sulu-Target-Group = regsub(req.http.Cookie, ".*_svtg=([^;]+).*", "1"); } elseif (req.restarts == 0) { set req.http.X-Sulu-Original-Url = req.url; set req.http.X-Sulu-Target-Group = regsub(req.http.Cookie, ".*_svtg=([^;]+).*", "1"); set req.url = "/_sulu_target_group"; } elseif (req.restarts > 0) { set req.url = req.http.X-Sulu-Original-Url; unset req.http.X-Sulu-Original-Url; } unset req.http.Cookie; } sub vcl_deliver { if (resp.http.X-Sulu-Target-Group) { set req.http.X-Sulu-Target-Group = resp.http.X-Sulu-Target-Group; set req.http.Set-Cookie = "_svtg=" + resp.http.X-Sulu-Target-Group + "; expires=Tue, 19 Jan 2038 03:14:07 GMT; path=/;"; return (restart); } if (resp.http.Vary ~ "X-Sulu-Target-Group") { set resp.http.Cache-Control = regsub(resp.http.Cache-Control, "max-age=(d+)", "max-age=0"); set resp.http.Cache-Control = regsub(resp.http.Cache-Control, "s-maxage=(d+)", "s-maxage=0"); } if (req.http.Set-Cookie) { set resp.http.Set-Cookie = req.http.Set-Cookie; header.append(resp.http.Set-Cookie, "_svs=" + now + "; path=/;"); } } zz
- 39. Sulu Docs
- 40. Good ol’ Javascript How to reevaluate target groups on cache hit?