The usual reason to move a domain from one application to another is that you have a major version of Drupal on one application (say, Drupal 7) and a different major version of Drupal on another application (say, Drupal 9), then it makes sense to develop them on separate codebases. Switching to that new site involves a few steps.

To prepare for the move, do the following:

• Check to see if you have the same load balancers for each application. You can determine this in the Servers section of each application's production environment.
• Plan to do this during a low-traffic period. The move will be slightly disruptive and there will be a very short period of time between the steps where the site will show Web Site Not Found. This is an unavoidable message, which should be very brief.
• Make sure your site's content editors are aware of the time window when you'll make the change.
• Each application will always be accessible at their acquia-sites.com domain no matter what DNS for the live domains are, so you can still make changes to each site that way if necessary.

These steps are something you can do a test run with using your non-production sites, assuming they have domains associated with them.

Prepare the SSL Certificates¶

Make sure you have uploaded the SSL certificate to the new application. You can (and should) do this before you move domains over, so that there are no errors relating to insecure pages after the switch.

1. Go into the SSL tab of the environment for the origin domain.
2. Click Show for each of the certificate, CA chain and private key.
3. Copy the text of each (do not share any of it via email or a ticket, keep it local to your computer).
4. Go into the SSL tab for the environment of the destination application.
5. Add a new SSL certificate and paste in the appropriate values.
6. Activate that certificate. It won't truly be active until you add the domains to that application (see below).

Moving over the Domain¶

If the load balancers are the same for each application, this will not require a DNS change. The steps are as follows:

1. Remove the domains from the old application through your the Domain Management tab of your old application.
2. As quickly as you can, add the domains to the new application's Domain Management tab.
3. There is no step 3.

If the load balancers are different for each application:

1. Remove the domains from the old application through your the Domain Management tab of your old application.
2. As quickly as you can, add the domains to the new application's Domain Management tab.
3. As quickly as you can after that, update the DNS for your domains to use the new load balancers' IP addresses . This will be subject to DNS propagation, which is usually fast, but also unpredictable. Use https://www.whatsmydns.net/ to see how that is proceeding once you make the change.

During the process if you encounter difficulties that you think are related to the platform, contact Acquia Support and we can take a look at what's going on.