Custom Varnish configurations are available only to Acquia Cloud Enterprise subscriptions with dedicated load balancers. Acquia Cloud Site Factory and Acquia Cloud Platform CDN do not support custom Varnish configurations.
For various reasons the Varnish caching layer might not be able to communicate with the back end. In that case the following error message will be displayed:
This server is experiencing technical problems. Please try again in a few moments. Thanks for your continued patience, and we're sorry for any inconvenience this may cause.
For example it could be that PHP has reached its maximum number of connections, or that a timeout in the code is preventing Apache from returning any Drupal content or that the web server is completely unresponsive.
This is sometimes called a "503 error" page. This message contains almost no styling or branding, and does not contain much information. When this happens, we strongly encourage you to look at your web server logs and if you can't determine a fix, to file a new critical support ticket.
If you would like a custom 503 error page, with links to resources that your site visitors can look at while work happens to restore the regular site, you need the following:
- You must be an Enterprise customer.
- You must have dedicated load balancers.
- Knowledge of VCL, the Varnish Configuration Language.
- Ask for and receive our default Varnish configuration file to modify.
This is described in greater detail in our documentation on custom VCL files.
If all of the above apply, you can edit the VCL file we provide in the places there is HTML code, and send that back to us for review.
We will then follow our deployment process for the custom VCL file and the next time the error happens, your website will show the customised error page.