We have an application hosted on AppEngine Flexible. It has multiple versions, primarily a master release and a staging develop version.
The master version has a domain pointed to it, but we can’t find a way of pointing a subdomain to the other version, so the only URL is has is like “develop-dot-appname-1234.appspot.com”
To make a “subdomain” using this format is to create a separate service and deploy it there. Of course, there are different ways of doing so, namely using the gcloud command[2] with the service names but others in the community have found a different approach as seen here[3].
There is also a dispatch file, where you use mappings in that file to point to a custom url[4].
There is a main document here[5], which tells how to map versions and services in many ways, namely mentioned URL or a dispatch file.
The only possibility I can think of from the above documentation is that we should deploy a service for each version with the name of that version, so that version “a” has service “a” and version “b” has service “b”. I don’t know if this causes other issues however.