Migrate to Helm's recommended standard labels

[cognifloyd]

Currently we have labeled our Deployments, Pods, and Jobs and other k8s resources with:

metadata:
  labels:
    app: st2auth # or st2api, st2actionrunner, st2web, etc
    tier: backend # or frontend
    vendor: stackstorm
    chart: {{ .Chart.Name }}-{{ .Chart.Version }}
    release: {{ .Release.Name }}
    heritage: {{ .Release.Service }}
spec:
  selector:
    matchLabels:
      app: st2auth
      release: {{ .Release.Name }}
  template:
    metadata:
      labels:
        # repeat the labels from above

We should migrate to the standard labels recommend in Helm's "Best Practices" doc.
https://helm.sh/docs/chart_best_practices/labels/#standard-labels

At a glance, I think these could work:

metadata:
  labels:
    app.kubernetes.io/name: st2auth # or st2api, st2actionrunner, st2web, etc
    app.kubernetes.io/component: backend # or frontend
    app.kubernetes.io/part-of: stackstorm
    app.kubernetes.io/version: {{ .Chart.AppVersion }}
    helm.sh/chart: {{ .Chart.Name }}-{{ .Chart.Version }}
    app.kubernetes.io/instance: {{ .Release.Name }}
    app.kubernetes.io/managed-by: {{ .Release.Service }}
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: st2auth
      app.kubernetes.io/instance: {{ .Release.Name }}
  template:
    metadata:
      labels:
        # repeat the labels from above

Both labels and label selectors would need to be updated.

A lot of charts define these labels in a helper template. It would be good to do the same in this chart to reduce the duplication.

[arm4b]

I found that many official charts at ArtifactHub are still following the old standards.

But sounds good!
It would make sense to switch from the old-style labels to the new recommended standards before the v1.0.0 release.

[arms11]

@cognifloyd would there be any negative impact on the existing resources running in the clusters?

[cognifloyd]

I don't know. I will test upgrading an st2 cluster (from old labels to new) to see what happens before I make the next PR.

[cognifloyd]

@arms11 In #351, I wrote a migration script to run before running helm upgrade. It adds the new labels before the upgrade so that helm can successfully identify the old resources it needs to update.

The plan is to release v0.110.0 (with #352) and then merge #351 to be included in the v1.0.0 release.