Feature request: support multiple notification urls

[ksurl]

Is your feature request related to a problem? Please describe.

can't specify more than one notification type (gotify, webhook, discord, pushover, email etc) for shoutrrr.

Describe the solution you'd like

support sending to more than url if specified

Describe alternatives you've considered

run 2 copies of watchtower with scoped labels but then you won't get notified on the same containers on both channels

Additional context

useful for backup notifications if one service is down

[piksel]

It's not stated in the docs, but you can supply --notification-url multiple times to add multiple notification targets. If you are using environment variables, just separate them with spaces, like this:

$ docker run --rm -it -v /var/run/docker.sock:/var/run/docker.sock \
  --env WATCHTOWER_NOTIFICATION_URL="logger: logger:" \
  containrrr/watchtower --notification-log-stdout --run-once
INFO[0001] Watchtower 1.5.1
INFO[0001] Using notifications: logger, logger
INFO[0001] Checking all containers (except explicitly disabled with label)
INFO[0001] Running a one time update.
Watchtower 1.5.1
Using notifications: logger, logger
Checking all containers (except explicitly disabled with label)
Running a one time update.
Watchtower 1.5.1
Using notifications: logger, logger
Checking all containers (except explicitly disabled with label)
Running a one time update.

Using the logger: notification service here as an example to show that it outputs every message twice (once per specified logger: URL).

[ksurl]

thanks.

[ghost]

To avoid important communication to get lost in a closed issues no one monitors, I'll go ahead and lock this issue. If you want to continue the discussion, please open a new issue. Thank you! 🙏🏼