Pantheon Advanced Page Cache

Pantheon Advanced Page Cache module is a bridge between Drupal cache metadata and the Pantheon Global CDN.

Just by turning on this module your Drupal site will start emitting the HTTP headers necessary to make the Pantheon Global CDN aware of data underlying the response. Then, when the underlying data changes (nodes and taxonomy terms are updated, user permissions changed) this module will clear only the relevant pages from the edge cache.

This module has no configuration settings of its own, just enable it and it will pass along information already present in Drupal 8 to the Global CDN.

If you want to take finer grain control of how Drupal is handling it's cache data (in ways that will interact with both the Global CDN and internal Drupal caches) consider using Views Custom Cache Tags and Cache Control Override.

This module is compatible with PHP 8.1-8.5.

BigPipe

Issue: The BigPipe module intercepts Drupal application requests, occasionally holding visitor sessions open indefinitely. On more complex Drupal applications, these open visitor sessions can result in a site's Redis layer experiencing memory exhaustion, cache corruption, and inability to serve web requests ("504 timeout" errors). Sites with BigPipe who are unable to serve web requests will also experience a lack of server-level traffic logs in the nginx-access.log file, and inhibiting traffic auditing.

Solution: Pantheon recommends disabling BigPipe for sites hosted on our platform. For sites with Pantheon Advanced Page Cache 2.3.4 installed, BigPipe is automatically disabled.

See Modules with known issues.

Debugging

By default, Pantheon's infrastructure strips out the Surrogate-Key response header before responses are served to clients. The contents of this header can be viewed as Surrogate-Key-Raw by adding on a debugging header to the request.

A direct way of inspecting headers is with curl -I. This command will make a request and show just the response headers. Adding -H "Pantheon-Debug:1" will result in Surrogate-Key-Raw being included in the response headers. The complete command looks like this:

curl -IH "Pantheon-Debug:1" https://dev-cache-tags-demo.pantheonsite.io/

Piping to grep will filter the output down to just the Surrogate-Key-Raw header:

curl -IH "Pantheon-Debug:1" https://dev-cache-tags-demo.pantheonsite.io/ | grep -i Surrogate-Key-Raw

Feedback and collaboration

Bug reports and feature requests should be posted in the Pantheon Github repository. For code changes, please submit pull requests against the Pantheon GitHub repository rather than posting patches to drupal.org.

Drupal 7 version

The Drupal 7 version of this module depends on the Drupal 8 Cache Backport module.