(If this plugin is of interest, you might like to join us at the Self Managed WordPress Group!)
Nginx FastCGI Purging is incredibly powerful, used appropriately static WordPress websites can handle enormous amounts of traffic and not choke.
That being said, fastCGI cache purging has always been a sticking point in it's implementation. Native Nginx FastCGI cache purging is one of the premium features of Nginx Plus, and as such users of the free platform have relied on third party modules to clear the cache when content updates.
The most commonly used module FRiCKLE's ngx_cache_purge module has been the go to recommendation of the community for some time, with Popular plugins such as Nginx Helper and Nginx Cache relying on this module to clear their cache.
For single user server stacks, where the Nginx Web Server user and the PHP web application user were one and the same, www-data or otherwise, this combination has been incredibly reliable and allowed many people to enjoy the awesome benefits of Nginx caching. It is worth noting that the RTCamp Nginx Helper plugin, when running on this Nginx build, will correctly function to do partial content-based purges in a multiuser (non www-data exclusive) Nginx environment.
But not all server stacks are born equal, many platforms employ a more dynamic set up where each web application has it's own user, this allows for servers to host multiple applications that each have different resource requirements, which is absolutely fantastic... but makes clearing the cache a nightmare. When installed on a WordPress site hosted on a multi-user stack, neither of the plugins mentioned above have the filesystem permissions to do a complete cache purge, and so for a long long time we have been SSHing into our servers and purging the cache with a bash command. (or using more exotic Lua or Golang based assistance - which is still pretty freaking awesome!)
This problem has gone unresolved for some time...
....well... not any more!
The Nginx FastCGI Cache Purger plugin, alongside a very specific Nginx compile and configuration, will allow your WordPress sites to clear their cache from within the WP-Admin.
The plugin is OOP but basic, it has been built as a foundation for others to take and do as they will. It has been provided to the community by a collaboration between GridPane and RunCloud, with me developing the plugin and working out how to implement it in WordPress based upon Jebat's identification of the correct module and call.
Currently, GridPane and RunCloud are only two VPS management platforms that I am aware of that utilise a compatible stack for this plugin.
With GridPane, everything comes configured and works out of the box, but RunCloud will require some slight updates to your Nginx Configuration if you have been using their published tutorial.
For WordPress users, you can easily pull apart the plugin source code and see what's going on, but the basics of the compile and configuration should work with any PHP application, I have purposefully used PHP Curl commands in the plugin so that the basics can be implemented in Laravel, Drupal or otherwise.
So....
First things first...
This plugin does NOT do incremental purging. It should be used alongside Nginx Helper, think of it as an Nginx Helper Helper for Multi User Nginx Stacks that are compiled with the Torden fork of the ngx_cache_purge module.
It does one thing, and one thing only... Purges all Nginx FastCGI cache for WordPress site from within that site's WP-Admin. Using this plugin alongside Nginx Helper means you will have both incremental cache purging when your site content updates, and the ability to purge all cache when you update non content based asset, for example theme assets.
Your Nginx compile needs to include the Torden Fork of ngx_cache_purge module, this will not work with the original FRiCKLE module.
The problem is, lots of pre built Nginx packages contain the ngx_cache_purge module, but how is one to know if yours is the right one?
In our case, we started from scratch and just made our own compile. An easy way to test is to use this plugin, and if it doesn't work, then you are using the 'other' ngx_cache_purge module.
Doing a recompile isn't too hard, there is a tonne of good material online.
I am not going to go into detail regarding all the Nginx Configurations required to properly tweak FastCGI caching
But it goes something like this:
http {
### Loads of other stuff above...
fastcgi_cache_path /var/run/nginx-cache levels=1:2 keys_zone=WORDPRESS:100m inactive=60m;
fastcgi_cache_key "$scheme$request_method$host$request_uri";
fastcgi_cache_use_stale error timeout invalid_header http_500;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;
### More stuff below....
server {
### Loads of other stuff above... don't forget that
set $skip_cache 0;
# POST requests and urls with a query string should always go to PHP
if ($request_method = POST) {
set $skip_cache 1;
}
if ($query_string != "") {
set $skip_cache 1;
}
# Don’t cache uris containing the following segments
if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
set $skip_cache 1;
}
# Don’t use the cache for logged in users or recent commenters
if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
set $skip_cache 1;
}
#### AND THIS BELOW FOR PURGE ALL
location ~ /purgeall {
fastcgi_pass php;
fastcgi_cache WORDPRESS;
fastcgi_cache_purge PURGE purge_all from 127.0.0.1;
}
#### And you'll need this for Nginx Helper purging on content update
location ~ /purge(/.*) {
fastcgi_cache_purge WORDPRESS "$scheme$request_method$host$1";
}
location ~ \.php$ {
#### Other stuff in your PHP block above
fastcgi_pass php;
fastcgi_cache_bypass $skip_cache;
fastcgi_no_cache $skip_cache;
fastcgi_cache WORDPRESS;
#### Maybe some other stuff below...
}
}
}
This block here is the key for purging all cache to work:
location ~ /purgeall {
fastcgi_pass php;
fastcgi_cache WORDPRESS;
fastcgi_cache_purge PURGE purge_all from 127.0.0.1;
}
Like any other WordPress plugin...
Go to it's settings page and click the big Purge button
So what is the purging mechanism?
Well it's a not-so-simple curl call to the server from local host, ie the site.
curl -L -X PURGE -H "Host:an-example.com" "https://127.0.0.1/purgeall" -k
The problem was that on HTTPS sites this wouldn't work without another if block and redirect within the server context, and using WordPress HTTP API for these sorts of mutant curl calls was driving me insane, so I fell back to PHP and CURLOPT_CUSTOMREQUEST, CURLOPT_FOLLOWLOCATION, CURLOPT_RETURNTRANSFER, and the secret sauce? ..... CURLOPT_RESOLVE for resolving the HTTPS calls.
So there you have it, feel free to use it, pull it apart and improve it. This has been a community problem and we would like it to remain a community solution, so we welcome any Pull Requests and contributions, it is our hope this plugin can be the foundation of something more functional in the long run that can better benefit everyone.
We have started a Facebook group for everyone who is rolling their own WordPress hosting solution using whatever tool of choice, all are welcome no matter if you use EasyEngine, ServerPilot, GridPane, RunCloud, or just pure terminal heroics. We invite anyone who reads this to join, if any of the above is pertinent to your needs then you are definitely one of us and we look forward to welcoming you.
