One of the problems that we ran into when moving to using containers was how to get the applications to connect. Let me explain the situation.
The applications in our production environment use DNS CNAME aliases that reference the production SQL instance’s IP address. In our old QA environment, the applications and SQL instance lived on the same virtual server so the DNS aliases were overwritten by host file entries that would point to 127.0.0.1.
This caused us a problem when moving to containers as the containers were on a separate server listening on a custom tcp port. Port numbers cannot be specified in DNS aliases or host file entries and we couldn’t update the application string (one of the pre-requisites of the project) so we were pretty stuck until we realised that we could use SQL client aliases.
This is definitely a place that you’d want to document changes thoroughly, as my experience is that relatively few DBAs would even think of looking there.