Ghost Silence: Some silences have been manually expired, but they will be recreated strangely

What did you do?

Initially, I create a long time silence (for forever silence), like this:

Matchers:
  environment=~.*uat.*|.*_preprod$
  alertsource!=monitor-zabbix
  cluster!=cloud-es
Duration: 999w

or

Matchers:
  environment="aws_sg_xxx_sdb"
Duration: 999w

A few months later, I deleted(expire) the silence manually.

But a few months later, the silence like a Ghost: it is recreated strangely. (I sware I didn't manually Recreate it!). And it's been repeated several times over the past year.

This caused some alerts (such as uat labels) not to be sent, and it took us a long time to find out that the problem was silence.

What did you expect to see?

Fix the problem.

What did you see instead? Under which circumstances?

See above.

Environment

• System information:

  Linux 3.10.0-1160.59.1.el7.x86_64 x86_64

• Alertmanager version:

alertmanager, version 0.24.0 (branch: HEAD, revision: [`f484b17`](https://github.com/prometheus/alertmanager/commit/f484b17fa3c583ed1b2c8bbcec20ba1db2aa5f11)) (Recently upgraded to v0.25.0 because of another issue)
build user: root@265f14f5c6fc
build date: 20220325-09:31:33
go version: go1.17.8
platform: linux/amd64

• Prometheus version:

  v2.39.1

• Alertmanager configuration file:

• Alertmanager CLI: (installed with Helm Chart)

alertmanager --storage.path=/alertmanager --config.file=/etc/alertmanager/alertmanager.yml --cluster.advertise-address=[10.244.14.187]:9094 --cluster.listen-address=0.0.0.0:9094 --cluster.peer=monitor-alertmanager-0.monitor-alertmanager-headless:9094 --cluster.peer=monitor-alertmanager-1.monitor-alertmanager-headless:9094 --cluster.peer=monitor-alertmanager-2.monitor-alertmanager-headless:9094 --data.retention=169h --web.route-prefix=/ --log.level=info

• Prometheus configuration file:

insert configuration here (if relevant to the issue)

Finally, if there is any information I can provide, please let me know.
In addition, the problem recurs over a long period of time and may not enable debug logging and continuous collection.

Thanks!

Start with the Alertmanager silence lifecycle in the supplied 0.24.0/0.25.0 clustered Helm deployment and CLI configuration; no source file or test is identified. Reproduce the long-lived 999w silence scenario and verify that a manually expired silence is not recreated and that matching alerts are delivered.