How to set up caching in Apache web server

Caching in Apache makes repeated requests cheaper by serving eligible responses from a local cache instead of regenerating them each time. A cache hit is the closest thing to free performance: lower latency for clients, lower load for the server, and fewer spikes that turn “fine” into “fire drill”. Static assets like CSS, JavaScript, fonts, and images usually benefit the most.

HTTP-aware caching in Apache is handled by mod_cache plus a storage provider such as mod_cache_socache (shared-object cache) or mod_cache_disk (disk cache). Caching is enabled for a specific URL space via CacheEnable, and cacheability is driven by standard HTTP rules (for example Cache-Control and Expires), not by blindly storing every response.

Cache scope matters more than cache size: caching personalized or authenticated content can leak private data or serve stale pages to the wrong client. The socache backend is shared-memory oriented, so entries are size-limited and large objects may be skipped; disk caching is a better fit for bigger files. Commands and paths below use the Ubuntu and Debian apache2 layout under /etc/apache2/.

1. Enable the required caching modules in Apache.

   $ sudo a2enmod cache cache_socache socache_shmcb expires headers
   Enabling module cache.
   Enabling module cache_socache.
   Enabling module socache_shmcb.
   Enabling module expires.
   Enabling module headers.
   To activate the new configuration, you need to run:
     systemctl restart apache2

   Systems with a2enmod support can enable modules without manually editing LoadModule directives.

   Related: How to enable or disable Apache modules

2. Open the Apache configuration file in a text editor.

   $ sudo vi /etc/apache2/apache2.conf

   Related: Location for Apache configuration

3. Add the required directives to enable and configure caching.

   <IfModule mod_cache.c>
       CacheQuickHandler off
       CacheLock on
       CacheLockPath "/tmp/mod_cache-lock"
       CacheLockMaxAge 5
    
       CacheHeader on
    
       <IfModule mod_cache_socache.c>
           CacheSocache shmcb:/var/cache/apache2/mod_cache_socache(20971520)
           CacheSocacheMaxSize 512000
           CacheSocacheMaxTime 86400
    
           <LocationMatch "\.(css|js|mjs|png|jpe?g|gif|svg|webp|ico|woff2?)$">
               CacheEnable socache
           </LocationMatch>
       </IfModule>
   </IfModule>

   Limit CacheEnable rules to public content, because cached responses can serve stale or private data if applied to personalized or authenticated URLs.

   Directive	Description
   CacheEnable	Enables caching for a URL space using a cache type such as socache.
   CacheSocache	Selects the socache provider and its arguments, such as shmcb:/var/cache/apache2/mod_cache_socache(20971520) to allocate a shared-memory cache in bytes.
   CacheSocacheMaxSize	Sets the maximum size (in bytes) of a single cached entry (headers + body).
   CacheSocacheMaxTime	Sets the maximum freshness lifetime (in seconds) of entries stored in socache.
   CacheHeader	Adds an X-Cache response header showing HIT, MISS, or REVALIDATE.
   CacheLock	Enables a per-URL lock to reduce backend stampedes while an entry is being filled or refreshed.
   CacheQuickHandler	Controls whether cached responses are served early in the request pipeline.

4. Set up cache control headers in .htaccess or a virtual host file for more granular control.

   <IfModule mod_expires.c>
     <FilesMatch "\.(css|js|mjs|png|jpe?g|gif|svg|webp|ico|woff2?)$">
       ExpiresActive On
       ExpiresDefault "access plus 1 month"
     </FilesMatch>
   </IfModule>

   Rules in .htaccess are ignored unless the relevant /<Directory>/ section permits AllowOverride for the required directive categories.

5. Test the Apache configuration for syntax errors.

   $ sudo apachectl configtest
   Syntax OK

   Related: How to test your Apache configuration

6. Restart Apache to apply the changes.

   $ sudo systemctl restart apache2

   Distributions using the httpd service name can restart using systemctl restart httpd.

   Related: How to manage the Apache web server service

7. Request a cacheable resource once to prime the cache.

   $ curl -I https://www.example.com/image.png
   HTTP/1.1 200 OK
   Date: Sat, 13 Dec 2025 09:13:40 GMT
   Server: Apache
   Last-Modified: Sat, 13 Dec 2025 08:57:56 GMT
   ETag: "1f61-603bb8a696d78"
   Content-Type: image/png
   Content-Length: 8033
   Cache-Control: max-age=2592000
   Expires: Mon, 12 Jan 2026 09:13:40 GMT
   X-Cache: MISS from localhost

   MISS is expected on the first request after a restart, because the cache starts empty.

8. Request the same resource again.

   $ curl -I https://www.example.com/image.png
   HTTP/1.1 200 OK
   Date: Sat, 13 Dec 2025 09:13:42 GMT
   Server: Apache
   Age: 2
   Content-Type: image/png
   X-Cache: HIT from localhost
   ##### snipped #####

   If X-Cache never changes to HIT, confirm the response is not marked no-store or private and matches the configured LocationMatch patterns.

   Disable cache debug headers after validation by setting CacheHeader to off.