Cloud Platform

Setting base URLs

This document contains information about setting base URLs without breaking non-production environments.


Occasionally, it may be necessary to set the $base_url value in a Drupal application’s settings.php file, because a contributed module may require this variable to be set, or an application may have specialized configurations.

Unfortunately, setting this variable can cause issues on Cloud Platform, where there are separate Development, Staging, and Production environments. If it is set unconditionally, the $base_url variable instructs Drupal to rewrite all requests for all environments, which breaks environments to which this variable doesn’t point.

The solution is to make use of the $_ENV['AH_SITE_ENVIRONMENT'] environment variable that is set by the Cloud Platform environment.

Note for multisite users

Multisite installations should set $base_url in a dynamic fashion, as outlined here. Setting the $base_url to an empty string disables caching and is not recommended.

Modify and use the following example code as necessary to fit your needs, and be sure to add your Remote Administration environment if your application has one:

if (isset($_ENV['AH_SITE_ENVIRONMENT'])) {
   switch ($_ENV['AH_SITE_ENVIRONMENT'])
        case 'dev': $base_url = '';
        case 'test': $base_url = '';
        case 'prod': $base_url = '';

You can further modify the preceding code if there are environments that don’t require $base_url to be explicitly set. For example, if the $base_url variable is required only for Production, you can use the following much shorter code snippet:

if (isset($_ENV['AH_SITE_ENVIRONMENT']) && $_ENV['AH_SITE_ENVIRONMENT'] === 'prod') {
  $base_url = '';


If you set a custom $base_url, be aware that the variable should not contain a trailing slash and should always start with either http:// or https://.