FastCGI Cache Purging for PHP-FPM

Ultra-fast caching for WordPress with automatic, surgical cache invalidation.

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• No Proxy Required

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  FastCGI cache talks directly to PHP-FPM—no reverse proxy overhead

• Microsecond Response

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  Cached pages served directly from memory or SSD by NGINX

• Selective Purging

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  Only changed pages are purged, rest of cache stays hot

• Built-in Security

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  Bypasses cache for logged-in users, admins, and WooCommerce carts

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When to Use FastCGI vs Proxy Cache

Feature	FastCGI Cache	Proxy Cache
Backend	PHP-FPM (direct)	Any HTTP backend
Latency	Lower (no proxy hop)	Slightly higher
Use case	WordPress, PHP apps	Node.js, Python, etc.
Config complexity	Simpler	More flexible

Use FastCGI cache if you're running WordPress or PHP directly on NGINX without a reverse proxy layer.

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Quick Setup

Step 1: Install Required Modules

# Install GetPageSpeed repository
dnf -y install https://extras.getpagespeed.com/release-latest.rpm

# Install cache purge module
dnf -y install nginx-module-cache-purge

Enable in /etc/nginx/nginx.conf:

load_module modules/ngx_http_cache_purge_module.so;

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Step 2: Configure FastCGI Cache

Add to your http block in /etc/nginx/nginx.conf:

# FastCGI cache zone definition
fastcgi_cache_path /var/cache/nginx/fastcgi 
                   levels=1:2 
                   keys_zone=WORDPRESS:100m 
                   max_size=10g 
                   inactive=60m 
                   use_temp_path=off;

# Cache key (what makes each cached page unique)
fastcgi_cache_key "$scheme$request_method$host$request_uri";

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Step 3: Configure Server Block

Create or update your WordPress server block:

server {
    listen 80;
    server_name example.com www.example.com;
    root /var/www/example.com;
    index index.php;

    # Cache settings
    set $skip_cache 0;

    # Don't cache POST requests
    if ($request_method = POST) {
        set $skip_cache 1;
    }

    # Don't cache URLs with query strings
    if ($query_string != "") {
        set $skip_cache 1;
    }

    # Don't cache WordPress admin, login, or specific paths
    if ($request_uri ~* "/wp-admin/|/wp-login.php|/xmlrpc.php|/wp-cron.php") {
        set $skip_cache 1;
    }

    # Don't cache for logged-in users or recent commenters
    if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_logged_in") {
        set $skip_cache 1;
    }

    # Don't cache WooCommerce pages
    if ($request_uri ~* "/cart/|/checkout/|/my-account/") {
        set $skip_cache 1;
    }
    if ($http_cookie ~* "woocommerce_cart_hash|woocommerce_items_in_cart") {
        set $skip_cache 1;
    }

    # Cache status header
    add_header X-Cache-Status $upstream_cache_status;

    # Enable PURGE method
    fastcgi_cache_purge PURGE from 127.0.0.1;

    location / {
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ \.php$ {
        try_files $uri =404;

        fastcgi_pass unix:/run/php-fpm/www.sock;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;

        # FastCGI caching
        fastcgi_cache WORDPRESS;
        fastcgi_cache_valid 200 60m;
        fastcgi_cache_valid 404 1m;
        fastcgi_cache_bypass $skip_cache;
        fastcgi_no_cache $skip_cache;

        # Important for dynamic content
        fastcgi_cache_use_stale error timeout invalid_header http_500 http_503;
        fastcgi_cache_lock on;
    }

    # Static files - no caching config needed
    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2)$ {
        expires 30d;
        add_header Cache-Control "public, immutable";
    }
}

Create cache directory and reload:

mkdir -p /var/cache/nginx/fastcgi
chown nginx:nginx /var/cache/nginx/fastcgi
nginx -t && systemctl reload nginx

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Step 4: Install WordPress Plugin

WordPress AdminWP-CLI

1. Go to Plugins → Add New
2. Search for "Proxy Cache Purge"
3. Install and activate

wp plugin install varnish-http-purge --activate

Configure the plugin:

1. Go to Settings → Proxy Cache Purge
2. Set Custom IP to 127.0.0.1
3. Save

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Step 5: Add Wildcard Purge Support

Create wp-content/mu-plugins/nginx-cache-purge-fix.php:

<?php
/**
 * Plugin Name: NGINX FastCGI Cache Purge Fix
 * Description: Appends wildcard to purge all cache variants
 */
add_filter("vhp_purgeme_path", function($purgeme, $schema, $host, $path, $pregex, $p) {
    if (empty($pregex)) {
        $purgeme .= "*";
    }
    return $purgeme;
}, 10, 6);

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Testing

# First request - should be MISS
curl -sI http://127.0.0.1/ -H 'Host: example.com' | grep X-Cache
# X-Cache-Status: MISS

# Second request - should be HIT
curl -sI http://127.0.0.1/ -H 'Host: example.com' | grep X-Cache
# X-Cache-Status: HIT

# Purge the cache
curl -sX PURGE 'http://127.0.0.1/*' -H 'Host: example.com'

# Verify purged
curl -sI http://127.0.0.1/ -H 'Host: example.com' | grep X-Cache
# X-Cache-Status: MISS

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How It Works

flowchart LR
    A["👤 Visitor"] -->|"GET /post/"| B["NGINX"]

    B -->|"Cache HIT"| C["⚡ Instant Response"]
    B -->|"Cache MISS"| D["PHP-FPM"]
    D --> E["WordPress"]
    E --> D
    D -->|"Store in cache"| B
    B --> C

    style A fill:#667eea
    style B fill:#009639,color:#fff
    style C fill:#48bb78,color:#fff
    style D fill:#4a90d9,color:#fff
    style E fill:#4a90d9,color:#fff

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Performance Comparison

Metric	No Cache	FastCGI Cache
Response Time	200-500ms	5-20ms
Requests/sec	50-100	5,000+
CPU Usage	High	Minimal
Memory	High (PHP)	Low (NGINX)

Real-world Impact

FastCGI cache typically improves WordPress response times by 10-50x and can handle traffic spikes without breaking a sweat.

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Advanced Configuration

Cache Different Durations by Content Type

# Cache pages for 60 minutes
fastcgi_cache_valid 200 60m;

# Cache redirects for 10 minutes
fastcgi_cache_valid 301 302 10m;

# Don't cache errors for long
fastcgi_cache_valid 404 1m;
fastcgi_cache_valid 500 502 503 504 0;

Serve Stale Content During Errors

fastcgi_cache_use_stale error timeout invalid_header 
                        updating http_500 http_502 http_503 http_504;

Cache Lock to Prevent Stampedes

fastcgi_cache_lock on;
fastcgi_cache_lock_timeout 5s;

When multiple requests hit an uncached page simultaneously, only one request goes to PHP-FPM. Others wait for the cache to populate.

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Troubleshooting

Pages not being cached

Check $skip_cache variable. Common issues:

• Query strings on all URLs (some plugins add ?ver= to pages)
• Cookies being set on all pages
• Check: curl -sI your-url | grep Set-Cookie

Logged-in pages being cached

Verify the cookie check includes your auth cookies:

if ($http_cookie ~* "wordpress_logged_in") {
    set $skip_cache 1;
}

Cache not purging

• Verify plugin setting: Custom IP = 127.0.0.1
• Check mu-plugin exists
• Test manually: curl -X PURGE http://127.0.0.1/page/

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Related

• Proxy Cache Guide

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  Alternative for non-PHP backends

  Proxy Cache

• cache-purge Module

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  Complete directive reference

  Documentation

• PageSpeed Module

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  Additional optimization layer

  Documentation