@kylecarbs and I were debugging a gnarly postgres issue over the weekend, and unfortunately it looks like it is still coming up occassionally:https://github.com/coder/coder/runs/5014420662?check_suite_focus=true#step:8:35 - so thought this might be a good testing Monday task.Intermittently, the test would fail with something like a `401` - invalid e-mail, or a `409` - initial user already created. This was quite surprising, because the tests are designed to spin up their own, isolated database.We tried a few things to debug this...## Attempt 1: Log out the generated port numbers when running the docker image.Based on the errors, it seemed like one test must be connecting to another test's database - that would explain why we'd get these conflicts! However, logging out the port number that came from docker always gave a unique number... and we couldn't find evidence of one database connecting to another.## Attempt 2: Store the database in unique, temporary folder.@kylecarbs and I found that the there was a [volume](https://github.com/docker-library/postgres/blob/a83005b407ee6d810413500d8a041c957fb10cf0/11/alpine/Dockerfile#L155) for the postgres data... so@kylecarbs implemented mounting the volume to a unique, per-test temporary folder in#89It sounded really promising... but unfortunately we hit the issue again!### Attempt 3... this PRAfter we hit the failure again, we noticed in the `docker ps` logs something quite strange:![image](https://user-images.githubusercontent.com/88213859/151913133-522a6c2e-977a-4a65-9315-804531ab7d77.png)When the docker image is run - it creates two port bindings, an IPv4 and an IPv6 one. These _should be the same_ - but surprisingly, they can sometimes be different. It isn't deterministic, and seems to be more common when there are multiple containers running. Importantly, __they can overlap__ as in the above image. Turns out, it seems this is a docker bug:moby/moby#42442 - which may be fixed in newer versions.To work around this bug, we have to manipulate the port bindings (like you would with `-p`) at the command line. We can do this with `docker`/`dockertest`, but it means we have to get a free port ahead of time to know which port to map.With that fix in - the `docker ps` is a little more sane:![image](https://user-images.githubusercontent.com/88213859/151913432-5f86bc09-8604-4355-ad49-0abeaf8cc0fe.png)...and hopefully means we can safely run the containers in parallel again.