subject of email notifications inconsistent across hosts/docker installs

[glc650]

Describe the bug

I'm using watchtower on two different hosts running two different docker instances. On one host, email notifications show the host name in the subject (Watchtower updates on <server_name>). On the other host, I get a string of numbers/letters instead (Watchtower updates on 28959a6d25cf)

To Reproduce

Just wait for notification to be sent (on container/docker startup or when image updates are detected).

Expected behavior

Show host name in subject of email notification (like watchtower does on my other host/docker install).

Environment

docker-compose.yml files:

The only differences are one is setup for monitor only while the other defaults to auto update with cleanup and removal of volumes unless container has the monitor only tag.

[piksel]

Watchtower uses the hostname that the environment supplies. Docker normally sets the hostname based on the UTS. My guess is that it uses host networking on one of the instances perhaps?

You can supply the hostname when starting a container with the --hostname argument (and optionally use $(hostname) to get the current systems hostname):

docker run -d \
  --hostname "$(hostname)"
  --name watchtower \
  -v /var/run/docker.sock:/var/run/docker.sock \
  containrrr/watchtower

Refer to the docker run docs.

[glc650]

Couldn't get $(hostname) to work with compose so I just set "hostname" manually and that did the trick.