Thanks to Peter who showed me that it idea in principle wasn’t entirely incorrect I’ve found the missing link. As a servicemonitor does monitor services (haha), I missed the part of creating a service which isn’t part of the gitlab helm chart. Finally this yaml did the trick for me and the metrics appear in Prometheus:
# Service targeting gitlab instances
apiVersion: v1
kind: Service
metadata:
name: gitlab-metrics
labels:
app: gitlab-runner-gitlab-runner
spec:
ports:
- name: metrics # expose metrics port
port: 9252 # defined in gitlab chart
targetPort: metrics
protocol: TCP
selector:
app: gitlab-runner-gitlab-runner # target gitlab pods
---
apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
name: gitlab-metrics-servicemonitor
# Change this to the namespace the Prometheus instance is running in
# namespace: default
labels:
app: gitlab-runner-gitlab-runner
release: prometheus
spec:
selector:
matchLabels:
app: gitlab-runner-gitlab-runner # target gitlab service
endpoints:
- port: metrics
interval: 15s
Nice to know: the metrics targetPort is defined in the gitlab runner chart.