To use mod_cache to cache dynamic content, the key is to correctly configure the HTTP cache control header and set the module parameters reasonably. 1. First, understand that mod_cache is cached based on Cache-Control, Expires and other response headers. You need to set a suitable header in a backend script (such as PHP), such as header('Cache-Control: max-age=3600, public'); 2. Enable mod_cache and related storage modules (mod_disk_cache or mod_mem_cache), and define the cache path, storage location and expiration time in the Apache configuration; 3. For content that changes according to the request header, the Vary header should be used correctly to distinguish the cache version, or personalized content should be excluded through CacheDisable and CacheIgnoreURLSessionIdentifiers; 4. Finally, verify and optimize the cache effect by curl testing response headers, monitoring cache hit rate, etc., and manually clean cache files if needed.
Caching dynamic content with mod_cache might sound tricky, but it's totally doable if you understand how it works and what settings make sense for your site. The main idea is that even dynamic pages — like those generated by PHP or other backends — can sometimes be cached, especially if they don't change every second or if they only change based on specific conditions.
1. Understand What mod_cache Does
First off, mod_cache isn't magic — it caches responses based on HTTP headers. That means if your backend sends the right cache control headers (like Cache-Control , Expires , or ETag ), Apache can decide whether to serve a cached copy or go to the origin server.
For dynamic content, this usually means setting appropriate caching directives in your backend scripts. For example, if you're using PHP, you might add something like:
header('Cache-Control: max-age=3600, public');
This tells Apache it's okay to cache that response for up to one hour.
Also, keep in mind that mod_cache works best when paired with mod_disk_cache or mod_mem_cache . You need to enable and configure at least one of these modules to actually store the cached content somewhere.
2. Basic Configuration Steps
Here's how to set up basic caching in your Apache config:
- Make sure the necessary modules are enabled:
-
a2enmod cache -
a2enmod disk_cacheormem_cache
-
- Add cache configuration to your virtual host or
.htaccessfile:
<IfModule mod_cache.c>
CacheEnable disk /
CacheRoot /var/cache/apache2
CacheDefaultExpire 3600
CacheMaxExpire 86400
</IfModule> This enables disk-based caching for all URLs ( / ), sets where to store the cache files, and defines default and maximum expiration times in seconds.
One thing to watch out for: mod_cache respects Cache-Control: no-cache or private headers. So if your app sends those, Apache won't cache the response — which is good for sensitive data, but might surprise you if you're trying to cache everything.
3. Handle Varying Content Carefully
Dynamic sites often generate different content based on request headers like Cookie or Accept-Language . By default, mod_cache doesn't account for this, so you'll want to use the CacheIgnoreHeaders directly carefully — or better yet, use Vary headers correctly in your backend.
For example, if you have a page that serves different content based on the user's language, you should include:
Vary: Accept-Language
That way, Apache will cache separate copies for each language instead of serving the wrong version to users.
If you're dealing with logged-in users or personalized content, consider excluding those paths from caching entirely:
CacheDisable /user/
Or use CacheIgnoreURLSessionIdentifiers to ignore things like session IDs in URLs that shouldn't affect caching.
4. Monitor and Test Your Setup
Once you've got caching enabled, test it. Use tools like curl to check response headers:
curl -I http://your-site.com/dynamic-page
Look for X-Cache: HIT or similar indicators (depend on your setup) to confirm that caching is working.
You should also monitor your cache performance. Tools like mod_status or external monitoring can help you see hit rates and adjust your cache size or TTLs accordingly.
Don't forget to clear the cache when needed — sometimes manually deleting files from CacheRoot is the easiest way during testing.
And that's basically it. It's not super complicated once you get the headers right and understand what Apache is doing under the hood.
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