Configuring the cache: rules, templates, file types and clearing the cache

The ShieldCache HTTP cache keeps content from your website ready. If a request is served from the cache, your server does not have to answer it. Pages with a login or shopping basket are not cached. You will find everything in the Cache tab with the sub-tabs Settings, Rules, File types and Purge.

Settings

• Cache active: When switched off, ShieldCache passes every request on to the origin.
• Cache duration of static files: for images, stylesheets, scripts and fonts. Stylesheets and scripts receive exactly this duration, all other static file extensions six times as long.
• Cache duration for HTML pages: The default is “Do not cache” - HTML then only comes from the cache if your server explicitly allows it via Cache-Control. With a duration, ShieldCache caches HTML even without this header.
• Respect cache control of the origin: recommended. If your server specifies Cache-Control for HTML, such as no-store or max-age, ShieldCache follows it. Responses with Set-Cookie are never cached.
• Cache duration in the browser: how long browsers keep static files themselves. Default: as specified by your server.
• Serve stale content: For this long after the cache duration has expired, ShieldCache still delivers the old version and fetches a fresh one in the background. If your server does not respond or responds with an error, the old version remains (default 6 hours, “Off” possible). Even when your server is working, the first visitor afterwards receives the old version once.
• Sort query parameters: /seite?a=1&b=2 and /seite?b=2&a=1 count as the same address.

Rules: paths, cookies and query parameters

Templates

There are templates for WordPress, WooCommerce, Shopware 6, Joomla and static websites. One click adds the application's usual paths, cookies and parameters to your rules. Check the suggestion, add your own cookies, for example from extensions, and click Save. The WordPress template, for example, excludes /wp-admin, /wp-login.php and /wp-json from the cache and adds the login and shopping basket cookies.

Paths without cache

Requests that begin with one of these paths always go to your server, for example /warenkorb/. Up to 50 paths are possible.

Cookies that bypass the cache

This setting is the most important one - and the one with the greatest impact:

• Empty list (default): Every request with a cookie bypasses the cache. Safe, but for websites that set cookies on every page, hardly anything will then come from the cache.
• List with entries: Only these cookies bypass the cache. ShieldCache removes all other cookies on page views - your server does not receive them.

The list must therefore contain all cookies your website needs for normal page views: login, shopping basket, session, language. A * at the end stands for any further characters, for example wordpress_logged_in_*. Forms (POST) always keep their cookies.

Remove query parameters

ShieldCache removes these parameters from the address, and your server does not receive them either. Only enter parameters that do not change the content, for example click identifiers such as _ga. ShieldCache removes utm_*, fbclid, gclid, msclkid, mc_eid and mc_cid anyway.

File types

In the File types sub-tab you specify which file extensions count as static files - they come from the cache without cookies and receive the long cache duration. Extensions that are not listed are treated like HTML. Under Never from the cache you enter extensions that always go to your server, for example pdf if your documents change frequently.

Clearing the cache

After an update or a correction, you clear the cache in the Purge sub-tab. This takes effect immediately, without applying:

• Everything: the entire cache of this site. Your server will be under more load for a short time afterwards.
• One path: exactly this path, with and without a query string, for example /style.css and /style.css?ver=2.
• Everything below a path: all addresses that begin like this, for example /bilder/.

Why does so little come from the cache?

If the statistics only show a small share from the cache, it is almost always due to one of these reasons:

1. Cookies: The list of bypass cookies is empty, and your website sets a cookie on every page. Then every request bypasses the cache. Use the matching template.
2. Set-Cookie: Responses that set a cookie are never cached - for example WordPress without cache rules.
3. Cache-Control: Your server sends no-cache or private. With “Respect cache control of the origin”, ShieldCache adheres to this.
4. HTML: The default is “Do not cache”. Set a cache duration for HTML if your pages are the same for all visitors.

The statistics point this out themselves when hardly any traffic comes from the cache, and link to the cache rules. More in Statistics and logs.