docker-mailman

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When connecting the mailman-core container to multiple networks — for example if the docker host uses one central database-container for multiple services — the autodiscovery of the MM_HOSTNAME variable here: https://github.com/maxking/docker-mailman/blob/master/core/docker-entrypoint.sh#L33 fails. In this case, hostname -i will return 172.19.199.2 <ip it got in the db network>, or similar depending on your configuration.

While this is workaroundable by setting a MM_HOSTNAME env manually, it’d be nice if multiple IPs could be detected and handled correctly ….

So, there is an interesting problem with having to use multiple IPs with Mailman Core.

Mailman Core listens for LMTP connections on $MM_HOSTNAME and it also uses the same value to generate alias_maps for MTA to contact Mailman Core at. It we choose a random IP from multiple outputs of hostname -i or use 0.0.0.0 (to listen on all available interfaces), MTA alias_maps will use those addresses (one of available interfaces/0.0.0.0) and they won't be able to reach Core.

I would like this hostname -i thing to actually go away completely and instead forward Ports from the container to host and then we can just use localhost everywhere.

Ran into this issue when adding a second docker network to the mailman-core container:

services:
  mailman-core:
[...]
    networks:
      mailman:
        ipv4_address: 172.19.199.2
      mailserver:   <========= Added

The second network is the one of the MTA (Postfix), so I could easily enable relaying outbound mail by just allowing relaying from this network in Postfix.

As soon as adding the second network, the REST API wasn't available anymore from mailman-web, although I could ping mailman-core.

I found out that adding the network changes the gunicorn log in mailman-core from: [2020-12-28 19:06:36 +0000] [40] [INFO] Starting gunicorn 19.9.0 [2020-12-28 19:06:36 +0000] [40] [INFO] Listening at: http://172.19.199.2:8001 (40)

to: 2020-12-30 16:59:43 +0000] [33] [INFO] Starting gunicorn 19.9.0 [2020-12-30 16:59:43 +0000] [33] [ERROR] Retrying in 1 second.

Setting MM_HOSTNAME=172.19.199.2 for mailman-core fixes the issue for me.

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