I am using the prometheus alertmanager that gets deployed by the kube-prometheus-stack helm deployment. Now I want to connect Grafana and tried to configure a alertmanager datasource what fails with the error message “Health check failed”.

I configured the URL as followed:
http://prometheus-alertmanager.default:9093

This URL/Port is reachable inside the kubernetes cluster (curl/wget works from my grafana-pod).

Any ideas on how to configure the alertmanager to be accessible by Grafana?