Add healthcheck command.

[Ryland0]

Is your feature request related to a problem? Please describe.
No problems.

Describe the solution you'd like
Add a healthcheck command to the image.

Describe alternatives you've considered
Not asking this question.

Additional context
Just curious if this has been discussed/considered.

[github-actions]

Hi there! 👋🏼 As you're new to this repo, we'd like to suggest that you read our code of conduct as well as our contribution guidelines. Thanks a bunch for opening your first issue! 🙏

[piksel]

Ref: https://docs.docker.com/engine/reference/builder/#healthcheck

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[simskij]

@piksel and I have been discussing this previously, and came to the conclusion that we don't really know what a healthcheck would even do in the watchtower case.

As watchtower runs on a scratch image, it means that watchtower crashing/not working will make the container exit and restart. Any suggestions?

[simskij]

No takers, so closing this.

[aehlke]

record exit codes from last runs (tmp files?), report latest as health check to catch scenarios such as lifecycle hooks failing

[PiDroid-B]

maybe something like that :

healthcheck.sh

#!/bin/sh

PERIOD_12H=43200

MAX_DELAY=$(( PERIOD_12H + 60 ))

# delay since last loop (seconds)
DELAY=$(($(date +%s) - $(date +%s -r /tmp/last_loop)))

[ "${DELAY}" -gt "${MAX_DELAY}" ] && exit 1

exit 0

And for the dockerfile :
HEALTHCHECK --interval=5m --timeout=2s --start-period=30s CMD sh healthcheck.sh

it's just an example to improve and adjust with env var. The watchtower job has just to make a touch on the file to update it