hostname not supported in --cluster.advertise-address

[pangorgo]

What did you do?

start alert manager with --cluster.listen-address=0.0.0.0:6783 --cluster.advertise-address=alertmanager.example.com:6783

What did you expect to see?

alertmanager starting normally

What did you see instead? Under which circumstances?

error in logs, when I put ip addr instead hostname, it works.

Environment

• System information:

Linux 3.16.0-4-amd64 x86_64

• Alertmanager version:

v0.15.0-rc.0

• Logs:

level=warn ts=2018-03-02T11:58:08.434627474Z caller=cluster.go:81 component=cluster err="couldn't deduce an advertise address: failed to parse advertise addr 'alertmanager.example.com'"
level=error ts=2018-03-02T11:58:08.435012167Z caller=main.go:166 msg="Unable to initialize gossip mesh" err="create memberlist: Failed to get final advertise address: Failed to parse advertise address \"alertmanager.example.com\""

[simonpasquier]

This is because cluster.advertise-address expects an IP address string, not a DNS name.
What would be the motivation for using a name?

[pangorgo]

Being in dynamic environment when I don't know IP address upfront?
And what is more, alertmanager is running as docker container so it is not easy for it to guess what is host address by doing sockaddr.GetPrivateIP()

[simonpasquier]

I'm not sure why you want to specify cluster.advertise-address in this case. If you leave it empty, it doesn't work? I did a quick test with 2 AlertManager containers running in the same Docker network and it worked fine for me.

[pangorgo]

Problem is that they don't run on the same docker network but on separate hosts.
I can use IPs, they are just less convenient in my case. It was just natural to me that if i can use hostname in cluster.peer I can expect the same for cluster.advertise-address.

[simonpasquier]

Ok I understand better now. How about resolving the host's IP address prior starting the container and passing it to the docker CLI (something similar to this)? Is this possible with your deployment model?

[calston]

That's not possible in Kubernetes.

[mxinden]

@calston When you are running on Kubernetes you can inject your Pod IP via a container environment variable definition:

        env:
        - name: POD_IP
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: status.podIP

        - --mesh.listen-address=$(POD_IP):6783