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@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](a83005b407/11/alpine/Dockerfile (L155)) for the postgres data... so @kylecarbs implemented mounting the volume to a unique, per-test temporary folder in https://github.com/coder/coder/pull/89
It sounded really promising... but unfortunately we hit the issue again!
### Attempt 3... this PR
After we hit the failure again, we noticed in the `docker ps` logs something quite strange:
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: https://github.com/moby/moby/issues/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:
...and hopefully means we can safely run the containers in parallel again.
