Templating external files in helm

Question

I want to use application.yaml file to be passed as a config map.

So I have written this.

 apiVersion: v1
 kind: ConfigMap
 metadata:
  name: conf
data:
{{ (.Files.Glob "foo/*").AsConfig | indent 2 }}

my application.yaml is present in foo folder and contains a service name which I need it to be dynamically populated via helm interpolation.

foo:
  service:
    name: {{.Release.Name}}-service

When I dry run , I am getting this

apiVersion: v1
kind: ConfigMap
metadata:
  name: conf
data:
  application.yaml: "ei:\r\n  service:\r\n    name: {{.Release.Name}}-service"

but I want name: {{.Release.Name}}-service to contain actual helm release name.

Is it possible to do templating for external files using helm , if yes then how to do it ? I have gone through https://v2-14-0.helm.sh/docs/chart_template_guide/#accessing-files-inside-templates I didn't find something which solves my use case. I can also copy the content to config map yaml and can do interpolation but I don't want to do it. I want application.yml to be in a separate file, so that, it will be simple to deal with config changes..

Answer 1

Helm includes a tpl function that can be used to expand an arbitrary string as a Go template. In your case the output of ...AsConfig is a string that you can feed into the template engine.

apiVersion: v1
kind: ConfigMap
metadata:
  name: {{ .Release.Name }}-conf
data:
{{ tpl (.Files.Glob "foo/*").AsConfig . | indent 2 }}

Once you do that you can invoke arbitrary template code from within the config file. For example, it's common enough to have a defined template that produces the name prefix of the current chart as configured, and so your config file could instead specify

foo:
  service:
    name: {{ template "mychart.name" . }}-service