>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3615287. --> Reported by: [luke.leber](https://www.drupal.org/user/3509746) >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p>There are two features that were added along the way, but are largely beneath the surface:</p> <ol> <li>The <code>cloudflare_purger.max_response_header_length</code> container parameter</li> <li>The <code>cloudflare_purger_cache_tag_prefix</code> setting</li> </ol> <p>These features should be documented.</p> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p>Add docs to the project page and possibly add a readme?</p> <pre>&lt;h4&gt;Dealing with hosting environment response header limitations&lt;/h4&gt;<br>&lt;p&gt;This module adds a "Cache-Tag" HTTP response header which may be very large on pages with many cache tags. Some web servers have strict limits on the size of HTTP response headers. Exceeding this limit can cause errors.&lt;/p&gt;<br><br>&lt;p&gt;To protect from this scenario, this module exposes a container parameter, &lt;code&gt;cloudflare_purger.max_response_header_length</pre><p>. If the Cache-Tag header for a response exceeds this value, the header is not set and the entire response is marked uncacheable by the Cloudflare CDN using the Cloudflare-CDN-Cache-Control header. <em>(Note - other caching layers may continue to cache the response!)</em>. Marking it uncacheable in Cloudflare is critical to prevent the page from being cached indefinitely as it won't have any of the cache tag metadata needed to support invalidations.</p> <h5>Example customization</h5> <p>Cloudflare supports individual response header sizes up to 16kB, but the Acquia hosting environment only supports header sizes of 8kB. In order to safely use this module with Acquia hosting, use this configuration in your <strong>services.yml</strong> file:</p> <pre> parameters: # 8192 - strlen("Cache-Tag: ") = 8181 cloudflare_purger.max_response_header_length: 8181 </pre><p> This ensures that the the Cache Tag header size remains compliant with both Acquia's origin servers and Cloudflare. </p> <h4>Preventing hash collisions if environments share a common zone</h4> <p>If multiple environments (dev / test / prod, for example) share a common Cloudflare zone and also share a common <strong>hash_salt</strong> setting, that would risk cross-environment cache purging. For such configurations this module supports a setting, <code>cloudflare_purger_cache_tag_prefix</code>, which can be used to override the cache tag prefix that is used to help ensure uniqueness of cache tags. By using this setting, each environment (dev / test / prod) can have its own unique cache tag prefix set, thus ensuring that cache purges do not break environment isolation.</p> <h5>Example custom prefixes (Acquia Hosting)</h5> <p>Say there are three environments: dev, test, and prod. There is also an environment variable that denotes which environment is which. By adding this to <strong>settings.php</strong>, each would have its own unique prefix.</p> <pre> if (isset($_ENV['AH_SITE_GROUP'], $_ENV['AH_SITE_ENVIRONMENT'])) { $settings['cloudflare_purger_cache_tag_prefix'] = $_ENV['AH_SITE_GROUP'] . '.' . $_ENV['AH_SITE_ENVIRONMENT']; } </pre><p> </p> <h3 id="summary-remaining-tasks">Remaining tasks</h3> <p>Review docs<br> Update the project page<br> Ship a readme? I'm neutral on this.</p>