AlertmanagerConfigs can't be created through the UI

[alemorcuq]

Setup

• Rancher version: 2.14.0 or newer
• Rancher Monitoring version: 109.0.0+up80.9.1-rancher.5 or newer
• Rancher UI Extensions: none?
• Browser type & version: irrelevant

Describe the bug
Using Rancher 2.14 and the Rancher Monitoring chart 109.0.0, AlertmanagerConfigs can't be created through the UI. This is because the Rancher Monitoring chart now includes a ValidatingWebhook to validate AlertmanagerConfigs and the YAML generated by the UI is not valid.

To Reproduce

1. Install Rancher Monitoring version 109.0.0 or newer
2. Go to Monitoring > Alerting > AlertmanagerConfigs and click Create
3. Set a name and click Create

Result
You will get the following error:

admission webhook "alertmanagerconfigsvalidate.monitoring.coreos.com" denied the request: AlertmanagerConfig is invalid

Expected Result
The AlertmanagerConfig should be created.

Screenshots

Additional context
As mentioned before, this is now an issue because AlertmanagerConfigs are now validated by a ValidatingWebhook.

There's two issues with the YAML that the UI generates:

apiVersion: monitoring.coreos.com/v1alpha1
kind: AlertmanagerConfig
metadata:
  name: test
  namespace: cattle-monitoring-system
spec:
  receivers:
  route:
    groupInterval: 5m
    groupWait: 30s
    repeatInterval: 4h
    match:
      {}
    matchRe:
      {}

1. spec.route.match and spec.route.matchRe do not exist in the CRD and should not be there
2. The route must define a receiver under spec.route.receiver and it must exist in spec.receivers, but the UI does not allow you to create a Receiver until the AlertmanagerConfig is created (the button to create a Receiver is disabled).

Both can be checked by applying the YAML manually via the console:

Error from server (BadRequest): error when creating "amc.yaml": AlertmanagerConfig in version "v1alpha1" cannot be handled as a AlertmanagerConfig: strict decoding error: unknown field "spec.route.match", unknown field "spec.route.matchRe"

Then if you remove those fields:

The "alertmanagerconfigs" is invalid: : root route must define a receiver

And after setting spec.route.receiver:

The "alertmanagerconfigs" is invalid: : receiver "test" not found

Example of a silly but valid YAML. spec.route.match and spec.route.matchRe are not present and the route references (spec.route.receiver) an existing receiver in spec.receivers.

apiVersion: monitoring.coreos.com/v1alpha1
kind: AlertmanagerConfig
metadata:
  name: test
  namespace: cattle-monitoring-system
spec:
  receivers:
    - name: test
  route:
    groupInterval: 5m
    groupWait: 30s
    repeatInterval: 4h
    receiver: test

[mallardduck]

Just a tiny bit more context - when we created the new 80.9.1 chart for 2.14 the updated chart added the mentioned new webhook. So this bug also is certainly in 2.14.0 which the chart launched with. The upstream commit that added the webhook is: prometheus-community/helm-charts@487bb85

[github-actions]

🤖 Issue grooming analysis

This issue is well-groomed and ready for triage. Here is a summary of each criterion:

Problem Statement ✅
The title clearly identifies the issue. The description explains that since Rancher Monitoring 109.0.0 introduced a ValidatingWebhook for AlertmanagerConfigs, the YAML generated by the UI is now rejected. Two specific root causes are identified: invalid fields being generated and a chicken-and-egg problem with receiver creation.

Acceptance Criteria ✅
The expected result ("The AlertmanagerConfig should be created") is supported by specific technical detail that makes "fixed" clear:

• The UI must not generate spec.route.match / spec.route.matchRe fields (not in the CRD).
• The UI must allow associating a Receiver with an AlertmanagerConfig before or during creation so that spec.route.receiver references a valid entry in spec.receivers.

Technical Details ✅
Webhook error messages, specific invalid YAML fields, kubectl validation errors at each step, and a working example YAML are all provided.

Reproducibility ✅
Numbered steps to reproduce are included with specific version requirements, a clear actual result (webhook denial error), and a clear expected result.

This analysis was generated automatically based on the repository's grooming checklist.

Generated by Daily Issue Grooming · ◷