Helm concatenated strings not being rendered-CodePudding

I'm working in a Chart template for managing deployments for different microservices apps.

On the values file the container Apps are declared in a list, as you can see:

# values.yaml
containerApps:
  - name: app1
    replicaCount: 1
    ...
  - name: app2
    replicaCount: 1
    ...
  - name: app3
    replicaCount: 1
    ...

The template reads the values-file definition in a loop that outputs the K8S YAML file.

{{- range $containerApp := .Values.containerApps }}
{{- with $containerApp }}
...
      containers:
        - name: {{ .name }}
          image: "{{ printf "$.Values.%s.image_repository" .name }}:{{ printf "$.Values.%s.image_tag" .name }}"
          replicas: {{ .replicaCount }}
          ...
...

Besides the values-file, we have also some values being declared using imperative approach via --set-string parameter.

helm template . --name-template my-app --namespace dev \
--set-string app1.image_repository=my-registry/image-app-1 \
--set-string app1.image_tag=073f799 \
--set-string app2.image_repository=my-registry/image-app-2 \
--set-string app2.image_tag=934df33 \
--set-string app3.image_repository=my-registry/image-app-3 \
--set-string app3.image_tag=k393caf... \
--values values.yaml

The problem is that helm doesn't seem to be able to render the template interpreting the $.Values.%s.image_repository" .name, generating a wrong output:

# What we expected:
image: my-registry/image-app-1:073f799
...
image: my-registry/image-app-2:934df33
...
image: my-registry/image-app-3:k393caf
...

# What we get...
...
image: $.Values.app1.image_repository:$.Values.app1.image_tag
...
image: $.Values.app2.image_repository:$.Values.app2.image_tag
...
image: $.Values.app3.image_repository:$.Values.app3.image_tag
...

We understand that maybe printf is not the way to go, and I've tried also index, which haven't work as well.

If you someone can give us a clue on how to get this working, it would be really appreciated.

Any idea is welcomed.

CodePudding user response：

As you observe, printf will produce a string but not evaluate it, which is why you're getting the template expressions directly in your output.

I would in fact use index here. I probably would do this by looking up the top-level value once, and then indexing within that.

{{- range .Values.containerApps }}
{{- $image := index $.Values .name }}
      containers:
        - name: {{ .name }}
          image: "{{ $image.image_repository }}:{{ $image.image_tag }}"
          replicas: {{ .replicaCount }}
{{- end }}

range already resets the special variable . to the list item, so you do not need the inner with (unless you expect the list items to potentially be empty). I set $image to the top-level item from .Values, and then when you need to use it, you can reference fields in it like $image.image_tag.