Update an array containing a parameterized value (and conditionally adding env to deployments)

[rrichardson]

I have a collection of manifests that I am mutating for a specific set of environments.
Specifically, a subset of these manifests are Deployments. I want to add an environment variable if it doesn't already exist. This poses 3 problems:

1. For each Deployment I want to update the spec/template/spec/containers/N where N.name == the metadata.name
2. In the Containers object in the deployment mentioned in update readme w/ travis #1, I want to add env if it doesn't already exist.
3. If env does exist, and the variable I want is present, I want to alter its value, if it's not present, I want to add a new element to the array that contains my intended name and value.

I thought I might be able to accomplish part one using vars, but I keep running into
Error: var '{DEPLOYMENT_NAME apps_v1_Deployment {metadata.name}}' cannot be mapped to a field in the set of known resources

The relevant part of my kustomize is:

vars:
  - name: DEPLOYMENT_NAME
    objref:
      kind: Deployment
      apiVersion: apps/v1
patches:
- path: setenv.yaml
  target:
    kind: Deployment

Then the setenv.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: placeholder
spec:
  template:
    spec:
      containers:
      - name: $(DEPLOYMENT_NAME)
        env:
        - name: NODE_ENV
          value: development

I am not sure what is causing the cannot be mapped to a field... error, but even if I got past that, I am assuming that I can't use $(DEPLOYMENT_NAME) as a selector.
Is there an alternate approach for this that might work?

After I accomplish that, how can I "upsert" both the env object and its contents?
In the approaches that I've tried, I can't seem to get kustomize to not just create another array entry so that the result ends up looking like

      containers:  
      - env: 
          name: NODE_ENV
          value: development
      - name: myintendedcontainer
         image: ...

Am I taking the wrong approach here? I would really like to avoid having to spell out a kustomization patch for every named deployment I am using.

[rrichardson]

Thinking about this more, I think that there is no good way in most merge languages to describe such a conditional inclusion into an array. Not with a single step, at least.

[monopole]

There's no notion of branching in kustomize - no way to check to see if a value exists and then do different things as a result.

this example has a description of merging configmap values as one goes up the overlay stack:
https://github.com/kubernetes-sigs/kustomize/blob/master/examples/combineConfigs.md

it should be easier to manage this you don't mind having more env vars defined for a particular container than the container actually needs

also, this might give you some ideas:
https://github.com/kubernetes-sigs/kustomize/blob/master/examples/valueAdd.md

[monopole]

please reopen if you have anything to add
there's also a notion of testing in IETF RFC 6902 (json)

[rrichardson]

@monopole - Thanks for your response. Do you think there is anything actionable that could be done after a test? Can it be used as conditional branches? It would be nice to have a boolean grouping in jsonpatch: e.g. { op: "and" : [ { op: "test" ...}, { op: "replace" ... }] }
I don't know if that would ever make it off the editing room floor in an RFC :)