Multiple Drupal sites in a single Project supports running multiple applications in the same project and these can be two or more Drupal site. But, they would be separate Drupal instances , they will have their assets separate and live their lives apart and it would be much better for them not to share the same database (though they could).

Note, that the same Drupal instance can also use multiple databases (just add multiple instances to services.yaml and use db_select) you will need to override settings.php as described here and add the other databases you could then use db_select to switch between those.

Old Style “Multisite” and actively discourages running Drupal in “multisite” mode. Doing so eliminates many of the advantages offers, such as isolation, safe testing, and so forth.

Additionally, because of the dynamic nature of the domain names that are created for the different environments the multisite configuration would likely be complex and fragile.

We recommend running separate projects for separate Drupal sites, or using one of the various “single instance” options available such as Domain Access, Organic Groups, or Workbench Access.

Using Domain Access has broad support for custom Drupal modules, including the Domain Access module.

If the multiple sites are part of the same project this makes sense.

Because of the dynamic nature of routes in, you’ll need to implement some logic (here you would replace MYMODULE with a convenient name of your own and include it in your custom modules for your Drupal installation).

 * Implements hook_domain_default_domains().
function MYMODULE_domain_default_domains() {
  $domains = array();
  $domains['wipe-domain-tables'] = 'wipe-domain-tables';

  $routes = (array) json_decode(base64_decode(getenv('PLATFORM_ROUTES')));

  if (!empty($routes) && is_array($routes)) {
    $weight = -1;
    foreach ($routes as $url => $route) {
      if (
        $route->upstream == 'drupal'
        && preg_match('/^(https?):\/\/([a-z0-9\.-]+)\/$/', $url, $matches)
        && preg_match('/^https?:\/\/([a-z]+).{default}\/$/', $route->original_url, $matches2)
      ) {
        $scheme = $matches[1];
        $domain_name = $matches[2];
        $machine_name = $matches2[1];

        $domains[$machine_name] = array(
          'subdomain' => $domain_name,
          'sitename' => MYMODULE_get_sitename($machine_name),
          'scheme' => $scheme,
          'valid' => 1,
          'weight' => $weight++,
          'is_default' => ($machine_name == 'www' ? 1 : 0),
          'machine_name' => $machine_name,

  return $domains;