Fix exim4 mail server

[khurtado]

Fixes dmwm/WMCore#12159

Issue: exim4-daemon-light is installed in local mode (mails for local users only). In order to send emails properly, we need to reconfigure into non-local mode and add back unix users created by the package.

[khurtado]

I have the following workaround for the exim4 mail server failing inside docker.

In general, the problem is related to the fact that some users are created at build time (exim4 creates a couple of users), that we lose when we bind mount the users from the host, but we need the latter in order to run as e.g.: cmst1, etc (since the host at CERN for example runs s-nail rather than exim4, their local users do not include anything related to exim4).

We also had issues with cron due to this bind mounting approach which we are working around already.

My opinion is that this change here should workaround exim4, but in the future a general solution would be to stop bind mounting /etc/group and /etc/passwd into the docker container and somehow create them at build time, in order to avoid services like cron or exim4 failing.

[todor-ivanov]

My opinion is that this change here should workaround exim4, but in the future a general solution would be to stop bind mounting /etc/group and /etc/passwd into the docker container and somehow create them at build time, in order to avoid services like cron or exim4 failing.

I completely agree with you Kenyi

[todor-ivanov]

looking good

[amaltaro]

@khurtado can you please also test this at FNAL? Once we confirm this is working in both CERN and FNAL (and virtual env, but Todor already confirmed it works for him), then we can move forward and also work on a new hot-patch for the agents.

[khurtado]

@amaltaro It seems I will need to work a bit more on this. The test at FNAL failed. The reason is both s-nail at the host and exim4 in docker are running on port 25 and we use the host network. I will need to work that around as well (in the config)