Website Caching Explained: From Browser Cache to Redis

Nginx, recommended cache headers

# /etc/nginx/conf.d/cache-headers.conf

# Static assets, cache for 1 year (they use hashed filenames)
location ~* \.(css|js|woff2|woff|ttf|eot)$ {
    expires 365d;
    add_header Cache-Control "public, immutable";
    add_header Vary "Accept-Encoding";
}

# Images, cache for 6 months
location ~* \.(jpg|jpeg|png|gif|webp|avif|svg|ico)$ {
    expires 180d;
    add_header Cache-Control "public";
}

# HTML, short cache with revalidation
location ~* \.html$ {
    expires 1h;
    add_header Cache-Control "public, must-revalidate";
}

# API responses, no cache
location /api/ {
    add_header Cache-Control "no-store, no-cache, must-revalidate";
}

Apache, .htaccess cache rules

<IfModule mod_expires.c>
  ExpiresActive On
  ExpiresByType text/css "access plus 1 year"
  ExpiresByType application/javascript "access plus 1 year"
  ExpiresByType image/webp "access plus 6 months"
  ExpiresByType image/jpeg "access plus 6 months"
  ExpiresByType image/png "access plus 6 months"
  ExpiresByType font/woff2 "access plus 1 year"
  ExpiresByType text/html "access plus 1 hour"
</IfModule>

<IfModule mod_headers.c>
  # Immutable for hashed assets
  <FilesMatch "\.(css|js|woff2)$">
    Header set Cache-Control "public, immutable, max-age=31536000"
  </FilesMatch>
</IfModule>

Nginx FastCGI Cache, server-level page caching

# In nginx.conf (http block)
fastcgi_cache_path /var/cache/nginx levels=1:2
  keys_zone=WORDPRESS:100m inactive=60m max_size=1g;
fastcgi_cache_key "$scheme$request_method$host$request_uri";

# In your server block
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 logged-in users
if ($http_cookie ~* "wordpress_logged_in") { set $skip_cache 1; }

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

location ~ \.php$ {
    fastcgi_cache WORDPRESS;
    fastcgi_cache_valid 200 60m;
    fastcgi_cache_bypass $skip_cache;
    fastcgi_no_cache $skip_cache;
    add_header X-FastCGI-Cache $upstream_cache_status;
    # ... standard PHP-FPM config
}

Recommended OPcache settings (php.ini)

; Enable OPcache
opcache.enable=1
opcache.enable_cli=0

; Memory, 256MB handles most WordPress sites + plugins
opcache.memory_consumption=256

; Max cached files (WordPress + plugins typically need 10,000+)
opcache.max_accelerated_files=20000

; How often to check for file changes (seconds)
; Production: 60+ (files rarely change)
; Development: 0 (check every request)
opcache.revalidate_freq=60

; Don't waste memory on comments (unless using annotations)
opcache.save_comments=1

; Huge pages (if supported by your OS)
opcache.huge_code_pages=1

; Preloading (PHP 8.0+), loads framework files at startup
; opcache.preload=/var/www/html/preload.php
; opcache.preload_user=www-data

Check OPcache status

# Check if OPcache is enabled
php -i | grep opcache.enable

# View detailed stats (create a PHP file)
<?php
$status = opcache_get_status();
echo "Memory used: " . round($status['memory_usage']['used_memory'] / 1024 / 1024, 2) . " MB\n";
echo "Hit rate: " . round($status['opcache_statistics']['opcache_hit_rate'], 2) . "%\n";
echo "Cached files: " . $status['opcache_statistics']['num_cached_scripts'] . "\n";

Install Redis and connect to WordPress

# Install Redis
sudo apt install redis-server -y

# Secure Redis, bind to localhost only
sudo nano /etc/redis/redis.conf
# Set: bind 127.0.0.1 ::1
# Set: maxmemory 128mb
# Set: maxmemory-policy allkeys-lru

# Start and enable
sudo systemctl enable redis-server
sudo systemctl start redis-server

# Test connection
redis-cli ping  # Should return PONG

# Add to wp-config.php (before "That's all, stop editing!")
define('WP_REDIS_HOST', '127.0.0.1');
define('WP_REDIS_PORT', 6379);
define('WP_REDIS_DATABASE', 0);
define('WP_REDIS_TIMEOUT', 1);
define('WP_REDIS_READ_TIMEOUT', 1);

# Then install "Redis Object Cache" plugin and click "Enable Object Cache"