Acquia recommends the following defaults for page caching rules in Edge CDN:

• Edge Cache TTL (Time To Live): 1 minute
• Browser Cache TTL: Respect Existing Headers

Respect Existing Headers will honor the user-defined Expires and Cache-Control headers. For more information, see Edge and Browser Cache TTL.

On occasion, an application may require a shorter Edge Cache TTL lifetime. If you reduce the amount of your Edge Cache TTL, be sure to change the Browser Cache TTL to the same value.

Edge CDN doesn’t enable Edge Cache TTL until the cache level is set. Select from the following available cache level options:

• Standard: This level is the recommended starting point, and is suggested for websites with frequent content updates, and a need for visitors to be displayed new content with low delay.
• Cache Everything: Select this option if you already know your website needs a greater level of caching.

You should also configure Page Cache Maximum Age (the amount of time assets are cached in Varnish® and Drupal) to your desired value, typically 30 minutes to one day. Edge CDN will contact Varnish at most once per minute for updated copies of that asset.

Updating cached content before expiration

If your content or assets have changed at origin (in your Drupal website), and you must update the cached copies of these assets before the Page Cache Maximum Age expiration date, Acquia recommends you use the Acquia Purge module.

After configuration, the Acquia Purge module will cause content updates to purge selected portions of Varnish cache. The next time Edge CDN requests the asset from Varnish, it will receive the newly updated content.

Cache tags on Acquia Edge

When purging caches on Edge CDN using the API or the dashboard, the Cache-Tag header (including whitespace and commas) must not exceed 255 bytes in total length after the header field name. If the supplied Cache-Tag header exceeds 255 bytes in length, only the tags in the first 255 bytes will be purged.

Caching recommendations for Acquia Edge