alertmanager down: couldn't deduce an advertise address: no private IP found, explicit advertise addr not provided

Summary

Standard install of gitlab omnibus ce gitlab-ctl status shows alertmanager to be "down, want up".

This has been reported before in https://gitlab.com/gitlab-org/gitlab-ee/issues/7376 and a workaround was provided in #3705 (comment 96944919) (also closed, no clue why).

The main problem that alertmanager is down has however not been addressed, so this is not fixed!

Also, the workaround now ceased to work with 12.1.1 (probably also 12.1.0) and breaks updates from 12.0.x (#3705 (comment 197308012)).

Steps to reproduce

see https://gitlab.com/gitlab-org/gitlab-ee/issues/7376

What is the current bug behavior?

Alertmanager is down, tries to restart once a second, logs error and wastes CPU.

What is the expected correct behavior?

Standard install with default config (wrt. prometheus and alertmanager) should just bring alertmanager up without any need for workaround. If it's ok to be down, don't bring it up by default?

Relevant logs

2019-07-29_16:38:50.75970 level=info ts=2019-07-29T16:38:50.759648241Z caller=main.go:177 msg="Starting Alertmanager" version="(version=0.16.2, branch=master, revision=)"
2019-07-29_16:38:50.75972 level=info ts=2019-07-29T16:38:50.759691431Z caller=main.go:178 build_context="(go=go1.11.10, user=GitLab-Omnibus, date=)"
2019-07-29_16:38:50.76406 level=warn ts=2019-07-29T16:38:50.763987126Z caller=cluster.go:154 component=cluster err="couldn't deduce an advertise address: no private IP found, explicit advertise addr not provided"
2019-07-29_16:38:50.76931 level=error ts=2019-07-29T16:38:50.769243825Z caller=main.go:202 msg="unable to initialize gossip mesh" err="create memberlist: Failed to get final advertise address: No private IP address found, and explicit IP not provided"
2019-07-29_16:38:51.80202 level=info ts=2019-07-29T16:38:51.801964401Z caller=main.go:177 msg="Starting Alertmanager" version="(version=0.16.2, branch=master, revision=)"
2019-07-29_16:38:51.80204 level=info ts=2019-07-29T16:38:51.802007118Z caller=main.go:178 build_context="(go=go1.11.10, user=GitLab-Omnibus, date=)"
2019-07-29_16:38:51.80733 level=warn ts=2019-07-29T16:38:51.807294014Z caller=cluster.go:154 component=cluster err="couldn't deduce an advertise address: no private IP found, explicit advertise addr not provided"
2019-07-29_16:38:51.81145 level=error ts=2019-07-29T16:38:51.811386606Z caller=main.go:202 msg="unable to initialize gossip mesh" err="create memberlist: Failed to get final advertise address: No private IP address found, and explicit IP not provided"
2019-07-29_16:38:52.84432 level=info ts=2019-07-29T16:38:52.844267217Z caller=main.go:177 msg="Starting Alertmanager" version="(version=0.16.2, branch=master, revision=)"
2019-07-29_16:38:52.84435 level=info ts=2019-07-29T16:38:52.844308751Z caller=main.go:178 build_context="(go=go1.11.10, user=GitLab-Omnibus, date=)"
2019-07-29_16:38:52.84875 level=warn ts=2019-07-29T16:38:52.848700006Z caller=cluster.go:154 component=cluster err="couldn't deduce an advertise address: no private IP found, explicit advertise addr not provided"
2019-07-29_16:38:52.85217 level=error ts=2019-07-29T16:38:52.851980241Z caller=main.go:202 msg="unable to initialize gossip mesh" err="create memberlist: Failed to get final advertise address: No private IP address found, and explicit IP not provided"

Details of package version

Provide the package version installation details

12.1.1-ce.0

Environment details

Operating System: Ubuntu
Installation Target:
- VM: proxmox
  - Resources
    - CPU: 4
    - Memory total: 12 GB
Installation Type:
- New Installation
- Upgrade from version 12.0.3
Is there any other software running on the machine: nope
Single node install

Configuration details

Provide the relevant sections of `/etc/gitlab/gitlab.rb`