Can I use functions from _helpers.tpl to fill out values.yaml in helm charts?

Question

Right now, I have a values.yaml with a section that looks a bit like this:

...
imageName:
  ports:
    - containerPort: 7980
      name: db0
      protocol: TCP
    - containerPort: 7981
      name: db1
      protocol: TCP
    - containerPort: 7982
      name: db2
      protocol: TCP
    - containerPort: 7983
      name: db3
      protocol: TCP
    - containerPort: 7984
      name: db4
      protocol: TCP
    - containerPort: 7985
      name: db5
      protocol: TCP
    - containerPort: 7986
      name: db6
      protocol: TCP
    - containerPort: 7987
      name: db7
      protocol: TCP
    - containerPort: 7988
      name: db8
      protocol: TCP
    - containerPort: 7989
      name: db9
      protocol: TCP
    - containerPort: 7990
      name: db10
      protocol: TCP
...

I'd like to clean this up by creating a function in _helpers.tpl that will take the min port value (7980) and the max port value (7990) and create the structure for each one in that format.

I am wondering: Is this possible? I am having a lot of trouble with this and using the helpers file in general so if anyone can nudge me in the right direction with how to accomplish this, I would appreciate that too!

Thanks :)

Answer 1

This should be possible. Say you configure your chart with the number of ports and the starting port:

# values.yaml (or a `helm install -f` values file)
numberOfPorts: 11
startingPort: 7980

You can use the until template function to turn that into a list of numbers:

{{- $dbs := until .Values.numberOfPorts }}

Now you can use the standard range function to loop over that list. Inside the loop body the value will be an integer from 0 to numberOfPorts - 1 and you can produce the list item accordingly. Also note that range takes over the . special variable, so you'll need to save anything you need from .Values outside the range loop.

imageName:
  ports:
{{- $startingPort := .Values.startingPort }}
{{- range $i := until .Values.numberOfPorts }}
    - containerPort: {{ add $startingPort $i }}
      name: db{{ $i }}
      protocol: TCP
{{- end }}