feat: patching chart without forking it

[mumoshu]

Use-cases

• Injecting Istio sidecars without mutating webhook and istioctl. You don't even need to fork upstream charts or modify your chart.
• Modify K8s resources produced by an upstream chart even if there's no configuration via values.yaml exposed.

Again this is a shameless plug: Adding helm-x integration to helmfile would allow you to apply patches(JSON Patch and Strategic-Merge Patch) before helm-installing it, and that's possible without modifying or forking it.

releases:
- name: myapp
   chart: sp/podinfo
   # version is required because it isn't provided by kustomization by its nature!
   version: 2.0.1
  patches:
  - jsonpatch.yaml
  - strategicmergepatch.yaml
  # inline json patch
  -  target:
      group: autoscaling
      version: v2beta1
      kind: HorizontalPodAutoscaler
      name: myapp-podinfo
    patch:
    - op: replace
      path: /spec/maxReplicas
      value: 1
  # inline strategic-merge patch
  - apiVersion: autoscaling/v2beta1
    kind: HorizontalPodAutoscaler
    metadata:
      name: myapp-podinfo
      labels:
        app: podinfo
        chart: podinfo-2.0.1
        release: myapp
        heritage: Tiller
    spec:
      scaleTargetRef:
        apiVersion: apps/v1beta2
        kind: Deployment
        name: myapp-podinfo
      minReplicas: 3

The patches setting results in running helm x upgrade --json-patch jsonpatch.yaml --strategic-merge-patch strategicmergepatch.yaml sp/podinfo --version 2.0.1 ...onhelmfile syncfor example, that has the same effect as running (1)helm template -o dir/to render the chart to a directory and (2) creratingkustomization.yamlwith all the rendered manifests in itsresources:section and corresponding patch definitions in it and (3) runningkustomize buildto apply patches to all the manifests in the dir and (4) finally installing it as a local chart by runninghelm upgrade temp/local/chart`.

See https://github.com/mumoshu/helm-x for more information.

[mumoshu]

In combination with helmfile's ability to apply templates on patches, this seems like a generalized version of #589. This isn't allow you to use istioctl kube-inject to inject sidecars, for example. But I believe you can write a patch to add a sidecar container to the pod spec of your choice.

[darkn3rd]

This is great, I have the same scenario (use case) with linkerd.