Formatting support for generated yaml

[jcristol]

When using the 1.0 installation of flux I have noticed that when the 1.0 flux controller updates the image version of a formatted manifest, the manifest in our case was formatted with prettier, flux doesn't change just the image tag it will enforce its own formatting probably based how the go-yaml package unmarshalls yaml.

What I would like is the ability to have a gitops flux repo where I can enforce formatting using a tool like prettier. I see two options where I can get this.

1. Add hooks in flux that allow us to run arbitrary commands on the modified yaml when an image patch is committed. This is a bit of a complex problem because the flux docker image wouldn't necessarily have the ability to run prettier so people that want to leverage this would have to run a baked version of the flux were they also install their formatter.

2. Get a better understanding on how flux is formatting the yaml files today and a means of replicating that with a formatter that I can invoke via bash against a yaml file. This way I could just make my repo formatter consistent with the formatting that flux will use when it generates yaml.

Concrete Example

apiVersion: apps/v1
kind: Deployment
metadata:
  annotations:
    fluxcd.io/automated: "true"
    fluxcd.io/tag.bar: glob:master-*
  labels:
    k8s-app: foo
  name: foo
  namespace: bar
spec:
  replicas: 2
  selector:
    matchLabels:
      k8s-app: foo
  template:
    metadata:
      labels:
        k8s-app: foo
      name: foo
    spec:
      containers:
        - env:
            - name: PORT
              value: "3000"
            - name: NODE_APP_INSTANCE
              value: "qa"
          image: foo:master-fdb57d8
          name: foo

the above was styled by prettier by running prettier ./file-name -w.
below was what flux will generate after bumping the image version.

Notice how the section starting with - env: is unindented.

apiVersion: apps/v1
kind: Deployment
metadata:
  annotations:
    fluxcd.io/automated: "true"
    fluxcd.io/tag.bar: glob:master-*
  labels:
    k8s-app: foo
  name: foo
  namespace: bar
spec:
  replicas: 2
  selector:
    matchLabels:
      k8s-app: foo
  template:
    metadata:
      labels:
        k8s-app: foo
      name: foo
    spec:
      containers:
      - env:
        - name: PORT
          value: "3000"
        - name: NODE_APP_INSTANCE
          value: "qa"
        image: foo:master-elka323d
        name: foo

More Color

I cannot configure prettier to match the current formatting that flux uses according to these issues prettier/prettier#4723 prettier/prettier#9355

[stefanprodan]

We use kustomize/kyaml to patch the YAML files, please comment on this issue kubernetes-sigs/kustomize#3559