LabelSelector MatchLabels are immutable

spec.selector.matchLabels are immutable in Daemonsets, Deployments etc

When creating a helm chart for an app, keep in mind that spec.selector.matchLabels is immutable and cannot be changed when upgrading the app.

If your app has been created from template-app, helper templates for creating labels and selector labels exist.

Example usage of label templates

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: {{ include "resource.default.name"  . }}
  namespace: {{ include "resource.default.namespace"  . }}
  labels:
    {{- include "labels.common" . | nindent 4 }}
spec:
  selector:
    matchLabels:
      {{- include "labels.selector" . | nindent 6 }}
  template:
    metadata:
      labels:
        {{- include "labels.common" . | nindent 8 }}
    spec:
      serviceAccountName: {{ include "resource.default.name"  . }}
      containers:
        - name: my-container
          image: "{{ .Values.Installation.V1.Registry.Domain }}/{{ .Values.image.name }}:{{ .Values.image.tag }}"
          imagePullPolicy: IfNotPresent

Re-enabling app upgrades without manual delete and re-create

Since the selector labels are immutable, it is not possible to do an usual app upgrade. Though it is possible to utilize helm chart hooks to resolve this by deleting the old release automatically.

For this, a pod running kubectl delete is created by helm before touching the rest of the charts resources.

A complete example of the required helm hooks can be found in this PR.