On Monday, 9 September 2019, Acquia will remove the option to bypass Varnish caching over SSL on the Acquia Cloud platform.
What does this mean for my application?
Currently the Acquia Cloud platform allows customer applications to bypass the Varnish caching layer when traffic is using TLS to connect to your application. When your application uses this configuration option, all traffic served via TLS hits your instance backend directly. This results in higher load on your application infrastructure and negates some of the performance and stability benefits Varnish caching provides.
We are implementing a change to the way traffic is served that will force all applications to utilize Varnish caching over SSL. This does not mean that all traffic must be cacheable. Bypassing Varnish caching for certain content or features of your application remains possible at the application level.
This change is part of our ongoing efforts to improve Acquia Cloud and enforce best practices on the platform, while ensuring that Acquia products and services are secure, reliable, and scalable.
How do I prepare for this change?
As of 9 September 2019, Varnish over SSL will be enabled for all customer applications on the Acquia Cloud platform. Applications already using this setting will not be affected.
We have reached out to all customers with applications that will be impacted by this change. If you have been contacted, you will need to take action prior to 9 September 2019 in order to ensure that your application continues to operate as expected. We encourage you to thoroughly test and make any necessary changes as soon as practicable. Preparing your application in advance will help ensure that it continues to perform as anticipated after this change. It will also provide time for our Support team to provide you support and guidance if additional application changes are required.
In most cases, enabling this feature will have no negative impacts for your application. Drupal and most modules already set the appropriate Cache-Control header. As a result, most customer applications will see a performance improvement as a result of this change Because implementing Varnish caching over SSL results in more traffic being cached, there will be less load to your database and file system infrastructures.
However, certain custom or in-house developed modules may not always set the appropriate “Cache-Control” header. This may result in unexpected content being cached once this feature is enabled. In these cases, applications may require additional code changes to ensure they continue to function as expected. Should you encounter any issues after enabling this feature, please file a Support request via the Acquia Support Help Center and one of our support engineers will be able to assist you further.
Bypassing Varnish at the Drupal application level
Drupal core and most contributed modules already set the appropriate Cache-Control header. However, Varnish caching can still be bypassed by configuring one of the following Drupal modules:
For further details, see Varnish: Bypassing the cache.
Additional resources providing further details on how Varnish caching works on the Acquia Cloud platform are available as follows: