How to Configure Nginx FastCGI Cache and ngx_cache_purge for WordPress

Recompiling Nginx to Add ngx_cache_purge Module

This guide explains how to recompile Nginx in an LNMP environment to add the ngx_cache_purge module and configure FastCGI caching for WordPress performance optimization.

Check Module Status

First, verify if the module is already installed:

nginx -V 2>&1 | grep -o ngx_cache_purge

If no output appears, proceed with installation.

Install ngx_cache_purge Module

Using LNMP 1.2 as an example (adjust paths for other versions):

1. Navigate to source directory and download module:

   cd /root/lnmp1.2-full/src
   wget http://labs.frickle.com/files/ngx_cache_purge-2.3.tar.gz
   tar xzf ngx_cache_purge-2.3.tar.gz
   cd nginx-1.8.0

2. Check current compilation arguments:

   nginx -V

   Copy the configure arguments line.

3. Add module to arguments and reconfigure:

   ./configure [your_copied_arguments] --add-module=../ngx_cache_purge-2.3

4. Compile without installing:

   make

5. Backup and replace binary:

   mv /usr/local/nginx/sbin/nginx{,_$(date +%F)}
   cp objs/nginx /usr/local/nginx/sbin

6. Verify installation:

   nginx -V 2>&1 | grep -o ngx_cache_purge

Configuring FastCGI Cache for WordPress

Cache Path Considerations

For optimal performance, place cache in tmpfs (memory filesystem):

• Faster: RAM access exceeds disk speed.
• Temporary: Data clears on reboot.
• Default paths: CentOS: /dev/shm/; Ubuntu/Debian: /run/shm.

Modify Nginx Configuration

Edit your site's Nginx config file (e.g., /usr/local/nginx/conf/vhost/site_name.conf).

Part 1: Cache Definition

fastcgi_cache_path /dev/shm/ levels=1:2 keys_zone=WORDPRESS:200m inactive=1d max_size=350M;
fastcgi_temp_path /dev/shm/temp;
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;

Part 2: Bypass Conditions

set $skip_cache 0;
if ($request_method = POST) { set $skip_cache 1; }
if ($query_string != "") { set $skip_cache 1; }
if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") { set $skip_cache 1; }
if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") { set $skip_cache 1; }

Part 3: PHP Location Block

location ~ [^/].php(/|$) {
    try_files $uri =404;
    fastcgi_pass unix:/tmp/php-cgi.sock;
    fastcgi_index index.php;
    include fastcgi.conf;
    fastcgi_cache_bypass $skip_cache;
    fastcgi_no_cache $skip_cache;
    add_header X-Cache "$upstream_cache_status From $host";
    fastcgi_cache WORDPRESS;
    fastcgi_cache_valid 200 301 302 1d;
}

Part 4: Cache Purging (Optional)

location ~ /purge(/.*) {
    allow 127.0.0.1;
    allow YOUR_SERVER_PUBLIC_IP; # Replace with actual IP
    deny all;
    fastcgi_cache_purge WORDPRESS "$scheme$request_method$host$1";
}

Save and restart Nginx: service nginx reload.

Handle tmpfs After Reboot

Add to /etc/init.d/nginx in the start section:

if [ ! -d '/dev/shm/your_cache_folder' ]; then
    mkdir /dev/shm/your_cache_folder
    chown -R ${user}.$user /dev/shm/your_cache_folder
fi

WordPress Configuration

Install Nginx Helper Plugin

Install and activate the Nginx Helper plugin from WordPress admin for automatic cache purging.

Modify wp-config.php

Add to your WordPress root wp-config.php:

define('RT_WP_NGINX_HELPER_CACHE_PATH', '/dev/shm');

Restart Nginx for changes to take effect.