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Custom Varnish configuration for Acquia Cloud Enterprise applications

This feature is available only to Acquia Cloud Enterprise subscriptions with dedicated load balancers.

This documentation page describes the specific Varnish® configurations allowed in Acquia Cloud.

Varnish Cache is a caching reverse proxy that is installed in front of all Acquia Cloud load balancing servers. For more information, see Using Varnish. Varnish Cache is configured with its own domain-specific programming language, VCL. If you are interested in deploying a custom Varnish configuration, contact Acquia Support. Acquia will provide you with a test environment for one week to test your new custom VCL, but coding and testing is the customer’s responsibility. For more complex changes, consider purchasing an Acquia Professional Services engagement.

Acquia Cloud Enterprise customers must contact Acquia support to create a support ticket to request a copy of the full VCL, based on their contractual NDA. Acquia does not disclose the configuration of our Nginx servers, as the configuration is both proprietary and subject to change without notice. Acquia Support does not provide support for specific VCL customizations.

Allowed Varnish configuration use cases

Here are some examples of use cases for which custom Varnish configurations can be useful:

  • Edge Side Includes (ESI) – Personalize fragments of pages based on Drupal 8 cache contexts and cache tags.
  • Site Error Pages (SEP) – Display customized error pages when the underlying layers of the application respond with HTTP 5xx errors. For more information, see Customized ACLs on Acquia Cloud.
  • Varnish Access Control Lists (vACL) – Whitelist or blacklist access to parts of a website by IP address or range. For more information, see Customized ACLs on Acquia Cloud.

Custom Varnish configuration schedule

Acquia deploys custom Varnish configurations on a weekly schedule. To deploy your custom Varnish configuration, you must meet the following weekly schedule:

  1. Contact Acquia Support to determine if one of the allowed VCL modifications is an appropriate solution for your needs.

  2. Request a copy of your current VCL from Acquia.

  3. Supply Acquia the list of environments in front of which you want to place the test load balancer.

  4. You can choose to either supply a new VCL file, or request to reinstate the default Acquia VCL, by Monday at 12:00 p.m. Eastern Standard Time (EST) (find UTC equivalent).

    • If you choose to supply a new VCL file, ensure that you supply the entire VCL file, and not only the lines that are changing.
    • If you choose to reinstate the default Acquia VCL, please explicitly indicate this request in your Support ticket. A VCL submission is not required.


    VCL files on Acquia Cloud are limited to a maximum of 128KB in size.

  5. Acquia deploys a test load balancer with the new VCL no later than 17:00 Eastern (North America) Time on Tuesday. You should then test to verify that the functionality is working as desired. To test the VCL on the test load balancer, it may be helpful to modify the /etc/hosts file on your local computer to point to the IP address of the test load balancer.

  6. If you encounter any issues that require a revised VCL, you must submit a revised VCL no later than 09:00 Eastern (North America) Time on Wednesday for Acquia to apply the revised VCL to the test load balancer.

  7. You must complete any testing and confirm your approval no later than 15:00 Eastern (North America) Time on Wednesday.

  8. Acquia performs code reviews between 15:00 Eastern (North America) Time on Wednesday and 15:00 Eastern (North America) Time on Thursday.

  9. VCL updates restart Varnish and clear Varnish cache. To minimize disruption, Acquia releases VCL files during non-peak periods, according to the following schedule:

    Region Data centers Time
    Asia-Pacific and Japan * AP-southeast-2, AP-southeast-1, AP-northeast-1 19:00-20:00 UTC Thursday
    Europe and Africa EU-central-1, EU-west-1 04:00-05:00 UTC Friday
    Americas SA-east-1, US-east-1, CA-central-1, US-west-2 07:00-08:00 UTC Friday

    * Default window

    Customers must specify the preferred window in the ticket for the custom VCL update. Once the custom VCL has been tested and approved by the customer, it will be added to the maintenance tasks scheduled for that window.

Requirements for Simple Error Pages on Acquia Cloud

Simple Error Pages (SEPs) that are provided as part of a custom VCL must meet the following criteria:

  • The file type must be HTML.
  • The file must be smaller than 10KB in size.
  • The file cannot contain links to external files, such as style sheets or images. External files are frequently unavailable when the backend layers of the application are unresponsive.
  • The file must include the specific Varnish error code to simplify troubleshooting.

Customized ACLs on Acquia Cloud

Custom Varnish access control lists (vACLs) provided as part of a custom VCL should have the following structure:

  • Multiple whitelist and blacklist rules may be created for each application.
  • Individual rules may be applied to multiple domain names on multiple environments.
  • Access control rules must be organized by domain name, and must not reuse domain name references.