Hello, @fendle
I believe that you are using the Deploy Mattermost on Docker documentation. Based on what we see here:
The docker app is unable to connect to the database server which is hosted on the mentioned port. May I know if you can go through the default steps mentioned in the documentation first to ensure that you are able to install it successfully first?
Since you mentioned that you are using your own PostgreSQL image, I just want to make sure if this is not a configuration issue. Thanks.