Add PodMonitor or ServiceMonitor outside of kube-prometheus-stack helm values - prometheus-operator

Question

Using kube-prometheus-stack helm chart, version 35.2.0. So far, I add my custom PrometheusRules, PodMonitor and ServiceMonitor via helm custom values.
helm install my-kubpromstack prometheus-community/kube-prometheus-stack -n monitoring \
-f my-AlertRules.yaml \
-f my-PodMonitor.yaml
Or in case of changes in the PrometheusRules or PodMonitor, I use helm upgrade. The custom values are defined based on kube-prometheus-stack/values.yaml. Where I define prometheus.additionalPodMonitors and additionalPrometheusRulesMap in separate YAML files
helm upgrade my-kubpromstack -n monitoring \
--reuse-values \
-f my-AlertRules.yaml \
-f my-PodMonitor.yaml
QUESTION: how to make the Prometheus server from kube-prometheus-stack aware of rules, podmonitor, servicemonitor created outside of the helm values?
For example, the PodMonitor definition below is NOT picked-up by Prometheus (ie doesn't appear in the targets in Prometheus UI).
kubectl apply -f - << EOF
apiVersion: monitoring.coreos.com/v1
kind: PodMonitor
metadata:
name: cluster-operator-metrics
labels:
app: strimzi
spec:
selector:
matchLabels:
strimzi.io/kind: cluster-operator
namespaceSelector:
matchNames:
- my-strimzi
podMetricsEndpoints:
- path: /metrics
port: http
EOF
The pod to monitor has a label strimzi.io/kind: cluster-operator and is located in my-strimzi namespace. I would expect the podmonitor above to be recognized by Prometheus automatically. Because the default podMonitorSelector: {} in kube-prometheus-stack/values.yaml has a comment that says:
## PodMonitors to be selected for target discovery.
## If {}, select all PodMonitors
EDIT: Looks like this question is useful to quite some people. The simplest solution is what Aris Chow suggested below. Set the custom helm values as below:
prometheus:
prometheusSpec:
podMonitorSelectorNilUsesHelmValues: false
probeSelectorNilUsesHelmValues: false
ruleSelectorNilUsesHelmValues: false
serviceMonitorSelectorNilUsesHelmValues: false

Answer 1

If you define prometheus.prometheusSpec.podMonitorSelectorNilUseHelmValues as false (in values.yaml, it is set to true by default) you could achieve your goal. As the value is true, it would just try to set a release label for matching PodMonitor, which your own definition does not include.
Or, you could leave it as true and set prometheus.prometheusSpec.podMonitorSelector as:
matchLabels:
prometheus: "true"
And add label prometheus: "true" in your podmonitor.yaml.
Click here to check the code if you are intereseted in details.
Please note that the chart version in this link is 15.4.4, you should change to the version you are using just in case there are any update.

Answer 2

Add this answer to address the question asked by a commenter in OP. Here is the PodMonitor definition I used + the custom helm values for the kube-prometheus-stack helm chart to have Prometheus operator discover the pod as target. The main point is the label app: strimzi. The comment section show how to configure helm to make Prometheus recognize that label.
#--------------------------------------------------------------------------------
# The kube-prometheus-stack helm chart must have the value
# podMonitorSelector.matchLabels set to match the label `app: strimzi` of the PodMonitors below.
# Otherwise Prometheus operator will not scrape the metrics of the corresponding pods
#
# prometheus:
# prometheusSpec:
# podMonitorSelector:
# matchLabels:
# app: strimzi
#--------------------------------------------------------------------------------
apiVersion: monitoring.coreos.com/v1
kind: PodMonitor
metadata:
name: strimzi-cluster-operator-metrics
labels:
app: strimzi
spec:
selector:
matchLabels:
strimzi.io/kind: cluster-operator
namespaceSelector:
matchNames:
- strimzi
podMetricsEndpoints:
- path: /metrics
port: http