15 December 2014

Caching Laravel with Varnish


PHP Framework popularity as at 2013 - Sitepoint
After having a very good experience with using Varnish to cache a Wordpress site we decided to look at caching Laravel.

Laravel always generates cookies regardless of whether a person is logged in or not.  This interferes with Varnish which by default will pass all requests with a cookie to the backend and skip the cache.

In our particular case our site supported the ability for users to login and would then present them with custom content.  This means that cookies are not restricted to a particular path so we can't discard cookies based on the request as we did for Wordpress when discarding everything except /wp-admin/* requests.

My solution was to use a package called session-monster ( Packagist ) which sets a response header if the data in the Laravel session can be ignored.  Varnish can detect this header and prevent the cookie from being set since we don't really need it.  This together with the varnish config below handily caches pages for all the users who are not logged in.

Unfortunately we're doing this as an afterthought to add value to a client and caching was not part of our original project design.  This means that there is not development time available to make use of edge side includes which would allow caching the parts of a page that are static even for logged in users.  Early proof of concept tests show that implementing ESI is not particularly difficult.  Here's a useful looking blog post on how to implement it.  Luckily in our case we don't expect there to be many logged in users compared to non.

So assuming that you've gotten your nginx, hhvm, and varnish up and running here is an example configuration file:

 backend default {  
  .host = "127.0.0.1";  
  .port = "8080";  
 }  
 acl purge {  
  "127.0.0.1";  
  "localhost";  
 }  
 sub vcl_recv {  
   # handle purge requests  
   if (req.request == "PURGE") {  
     if (!client.ip ~ purge) {  
       error 405 "Not allowed.";  
     }  
     ban("req.url ~ "+req.url+" && req.http.host == "+req.http.host);  
     error 200 "OK";  
   }  
   if (req.url ~ "\.(png|gif|jpg|swf|css|js)$") {  
     return(lookup);  
   }
    # the cookie will persist until it expires (see your laravel session config)
    if (req.http.Cookie ~ "laravel_session") {
     return(pass);
    }   
    # else ok to fetch a cached page  
   return (lookup);  
 }  
 sub vcl_fetch {  
   # strip the cookie before the static file is inserted into cache.  
   if (req.url ~ "\.(png|gif|jpg|swf|css|js)$") {  
     unset beresp.http.set-cookie;  
   }  
   # remove some headers we never want to see  
   unset beresp.http.Server;  
   unset beresp.http.X-Powered-By;  
   unset beresp.http.X-Pingback;  
   set beresp.do_esi = true; /* Do ESI processing */  
   set beresp.ttl = 10m;  
   # don't cache response to posted requests or those with basic auth  
   if ( req.request == "POST" || req.http.Authorization ) {  
      return (hit_for_pass);  
   }  
   # Laravel always adds a session cookie - we remove it with session monster and check it here  
   # Do this before checking the page state but after post  
   if (beresp.http.X-No-Session ~ "yeah") {  
     unset beresp.http.set-cookie;  
   }  
   else
   {
       # do not cache responses which are for logged in users
       return (hit_for_pass);
   }
   # only cache status ok  
   if ( beresp.status != 200 ) {  
     return (hit_for_pass);  
   }  
   # else ok to cache the response  
   return (deliver);  
 }  
 sub vcl_deliver {  
   if (obj.hits > 0) {  
     set resp.http.X-Cache = "HIT";  
   }  
   else {  
     set resp.http.X-Cache = "MISS";  
   }  
   unset resp.http.Via;  
   unset resp.http.X-Varnish;  
 }  
 sub vcl_hit {  
  if (req.request == "PURGE") {  
   purge;  
   error 200 "OK";  
  }  
 }  
 sub vcl_miss {  
  if (req.request == "PURGE") {  
   purge;  
   error 404 "Not cached";  
  }  
 }  

Installing the Laravel side of things is simple:
  1. Add a require for session monster to your composer file ( "haifanghui/session-monster": "dev-master" )
  2. Edit your application config and include the provider as in the snippet below
  3. Edit app/config/session.php and set the session lifetime to a number you feel comfortable with
   'providers' => array(  
     'HaiFangHui\SessionMonster\SessionMonsterServiceProvider'  
   ),  
You need to set the session timeout so that the cookie expires sometime after the user logs out.  Even though Laravel will stop emitting the cookie when the user logs out the browser will keep sending it and breaking the cache.  
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