Docker image prom/alertmanager:v0.27.0 fails to parse webhook_url_file from msteams_config

[martipoe]

What did you do?

I tried to use the latest Docker Image prom/alertmanager:v0.27.0 with a webhook_url_file in https://prometheus.io/docs/alerting/latest/configuration/#msteams_config, because the feature should be supported for 0.27.0 according to the Changelog.

What did you expect to see?

Prometheus should be able to read the URL from webhook_url_file.

What did you see instead? Under which circumstances?

The docker container displays the error and keeps restarting:
ts=2024-06-23T20:09:11.319Z caller=coordinator.go:118 level=error component=configuration msg="Loading configuration file failed" file=/etc/alertmanager/alertmanager.yml err="no msteams webhook URL provided"

This issue does not occur with prom/alertmanager:main, then the webhook_url_file is read successfully.

Environment

• Alertmanager version:

alertmanager, version 0.27.0 (branch: HEAD, revision: 0aa3c2aad14cff039931923ab16b26b7481783b5)
  build user:       root@22cd11f671e9
  build date:       20240228-11:51:20
  go version:       go1.21.7
  platform:         linux/amd64
  tags:             netgo

• Alertmanager configuration file:

...
receivers:
  # https://prometheus.io/docs/alerting/latest/configuration/#msteams_config
  - name: 'MicrosoftTeamsTEST'
    msteams_configs:
      - webhook_url_file: "/etc/alertmanager/secrets/webhook_test"
        send_resolved: true
...

[grobinson-grafana]

I think there was a bug in 0.27.0 which prevents this from working (see #3728). The fix should be in the next release. However, I'm not sure when that will be, so you might need to keep using the main image until 0.27.1 is released.

[TornaxO7]

Funny enough, webhook_url_file also fails for the discord_config.

EDIT:
Well, I just realized that the author of the PR added this information to the title as well...