Share users database from one Drupal database with other Drupal Installs (separate databases, not just prefixed tables in the same db) I have several Drupal databases and core sites currently. What I want to have is several Drupal databases that share a common users database under one core site source. The reason I want this is so that I can restore a sites database from any date I choose without rolling back the other sites content as well. I have looked into prefixing but it sounds like all sites have to be under the same database, the same seems to be true of domain access.
Instead of using table prefixes, you can use a reference to another database as a prefix. For example, core database holds the shared users / permissions, drupal_website database is your actual website.



$databases['default']['default'] = array(
    'driver' =&gt; 'mysql',
    'database' =&gt; 'drupal_website',
    'username' =&gt; 'db_username',
    'password' =&gt; 'db_password,
    'host' =&gt; 'ip_db_server',
    'prefix' =&gt; array(
         'default' =&gt; '',
         'users' =&gt; 'core.',
         'users_roles' =&gt; 'core.',
         'sessions' =&gt; 'core.',
         'role' =&gt; 'core.',
         'role_permission' =&gt; 'core.',
         'authmap' =&gt; 'core.',
    ),
);


Minor drawback, your database needs to be stored on the same mysql server and each database uses the same credentials (username / password) for the connection.