Karma is unable to resolve info from alertmanager through seed proxy

[michalvanco]

User Story
After installing the MLA stack according to documentation, karma pod is logging following error:

{"level":"error","error":"request to http://seed-proxy-kubermatic.kubermatic.svc.cluster.local:8001/api/v1/namespaces/monitoring/services/alertmanager:web/proxy/metrics failed with 403 Forbidden","alertmanager":"kubermatic","uri":"http://seed-proxy-kubermatic.kubermatic.svc.cluster.local:8001/api/v1/namespaces/monitoring/services/alertmanager:web/proxy/","message":"Request failed"}
{"level":"error","error":"response status code does not match any response statuses defined for this endpoint in the swagger spec (status 403): {}","alertmanager":"kubermatic","message":"Collection failed"}

And karma UI display such error (403) as well.

Issue is coming from this place: https://github.com/kubermatic/kubermatic/blob/master/pkg/controller/master-controller-manager/seed-proxy/resources.go#L381

After setting the --accept-hosts='^.*' it works.

Environment

• KKP 2.18.1
• k8s 1.22.2 (or 1.21.5)

Acceptance criteria
Karma pod is working out of the box on the common KKP installation and it's possible to see alerts from alertmanager.