Acquia Cloud Sticky Sessions

Deprecated in favor of Alternative Stream Wrappers.

The Acquia Cloud Enterprise high-availability architecture uses two or more load balancing servers to handle incoming requests, routing them to the site's web servers in a way that shares the load across multiple web servers.

For some use cases, however, this can lead to problems. For example, when you use a module like Plupload to upload a large file, the file is divided into chunks that upload separately. On Acquia Cloud Enterprise, the user's requests could get switched from one web server to another during the upload. As a result, chunks of the uploaded file could arrive on different web servers, and the web servers would not be able to put them back together.

To solve this problem, use the Acquia Cloud Sticky Sessions module. When you download, install, and enable this module, the following occurs:

• Your site defines a new permission named Stick to Acquia web node. For any user with that permission, your site sets a cookie named ah_app_server. The cookie is deleted when the user logs out.
• When your Acquia Cloud Enterprise load balancers see the ah_app_server cookie, they direct the request to a single web server. This ensures that all upload requests are sent to the same web server, and the chunks of an uploaded file can be successfully combined.

To use the Acquia Cloud Sticky Sessions module:

1. Download and install the module.
2. Enable it on your Drupal site.
3. On your Drupal site's People > Permissions page, assign the Stick to Acquia web node permission to the appropriate roles on your site. Typically, this includes the admin users or other users who you want to be able to upload large files regularly, and should not include anonymous users.