Having long cache lifetimes and expire times has major advantages, which means that it’s important to use Varnish® with Drupal for performance improvements. However, when changes are made or new content is published, you don’t want to wait a long time for visitors (including non-authenticated users) to see the changes. In these cases, you should periodically purge your Varnish cache.
Varnish excels at storing pages, CSS, JavaScript files, and multimedia files for as long as possible, so that visitor requests don’t hit the back-end (in most scenarios, this will be Apache). This greatly helps with performance and allows an application to scale much better than it would if only Apache was serving pages. When your organization decides to implement a caching strategy, you will need to explore all available options and decide what’s best for your situation. For more information, see Using Varnish.
Select from the following methods to purge your Varnish cache:
Using Acquia Purge
The Acquia Purge module is the fastest and most convenient way to purge Varnish cache on Cloud Platform. Acquia Purge works within your Drupal application to clear Varnish cache on Cloud Platform and works with other modules to update caches and external caching layers.
To update Varnish and external caching layers with updated content for the current Drupal version, use the Purge and Acquia Purge modules. For more information, see Installing Acquia Purge.
Troubleshooting
For the official documentation for the Acquia Purge module, go to Drupal.org. You should file any module specific issues on Drupal.org. For Acquia Support related issues, create a Support ticket.
Purging programmatically
While Acquia Purge is the best method when it comes to implementing a caching strategy, another good method is to use the Purge and Cache Expiration modules.
The Purge module clears URLs from reverse proxy caches like Varnish and also issues an http PURGE request to them. It works with the Cache Expiration module to act on events that are likely to expire URLs from the proxy cache and interact with Rules and Drush. This results in delivering faster content updates to end users. Acquia Purge is recommended on Cloud Platform because it has many of the same features, and the maintainers for Purge and Acquia Purge work closely to ensure compatibility.
If you absolutely must purge a page manually from Cloud Platform, you can learn how to manually purge a page.
Using Cloud Platform Hooks
Cloud Hooks allow you to automate almost anything as part of your workflow actions. A Cloud Hook is a script in your code repository that Cloud Platform executes on your behalf when a triggering action occurs (for example, when a database, some code or some files are copied from one environment to the other). You can implement Cloud API Varnish cache clears as part of Cloud Hooks triggers. For example, when you are deploying code from the Development to the Staging.
For more information about Cloud Hooks, see Automating with Cloud Hooks, and Cloud Hooks GitHub repository.
Using other purge methods
Although Acquia Purge is the preferred and safest method of cache purging, there are some other methods that you can use if necessary: