I want to reduce copy/paste and have my environments (where I use kustomize) get an alerting rule from the base and then just provide the value.

base/prometheus-alerts.yaml

apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  labels:
    release: kube-prometheus-stack
    role: app-rules
    test: $(VAL_A) # This works
  name: xx
  namespace: monitoring
spec:
  groups:
    - name: xx
      rules:
        - alert: xx
          annotations:
            description: 'xx'
          expr: sum(rate(xx[5m])) by (container) < $(VAL_A) # This does not

In my testing env I have the following
kustomization.yml

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization
resources:
  - ../base
vars:
- name: VAL_A
  objref:
    kind: PrometheusRule
    name: connectors-taz-tcp-alerts
    apiVersion: monitoring.coreos.com/v1
  fieldref:
    fieldpath: data.VAL_A

And then the patch-prometheus-alerts.yaml

apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: connectors-taz-tcp-alerts
  namespace: monitoring
data:
  VAL_A: "hello-world"

Whenever I run kubectl kustomize . I will get the following:

apiVersion: monitoring.coreos.com/v1
data:
  VAL_A: hello-world
kind: PrometheusRule
metadata:
  labels:
    release: kube-prometheus-stack
    role: app-rules
    test: hello-world
  name: xx
  namespace: xx
spec:
  groups:
  - name: xx
    rules:
    - alert: xx
      annotations:
        [..]
          expr: sum(rate(xx[5m])) by (container) < $(VAL_A)

Why is the label test changed to “hello-world” but not the $(VAL_A) in the expression?