If condition checking value returned by helm template

Question

I have a parent chart with 2 subcharts. The parent chart has global.myflag while the subcharts have myflag fields, in their respective values.yaml. I want the flexibility, where the sub-charts could be deployed independently. So, I have added a template function in the sub-chart _helper.tpl where I want to check - if global.myflag exists, use that value - else use value of myflag from the subchart

The template will return true/false. Something like this -

{{- define "isFlagEnabled" -}}
{{- $flag := false -}}
{{- if .Values.myflag -}}
{{- $flag := .Values.myflag -}}
{{- end -}}
{{- if .Values.global.myflag -}}
{{- $flag := .Values.global.myflag -}}
{{- end -}}
{{- printf "%s" $flag -}}
{{- end -}}

And using this value (true/false), I want to set some values in my config.yaml.

{{- if eq (value from template) true -}}

I am having two questions here - 1. Can we do 'if' condition on the template values? How? 2. Is there a better way to do this?

Answer 1

Definition of isFlagEnabled template

Retouched and cleaned your function

{{- define "isFlagEnabled" -}}
{{- if .Values.global -}} {{/* <-- check parent exists to avoid nil pointer evaluating interface {}.myflag */}}
{{- if .Values.global.myflag -}}
{{- .Values.global.myflag -}}
{{- end -}}
{{- else if .Values.myflag -}} {{/* <-- make sure its else if so you wont override if both defined */}}
{{- .Values.myflag -}}
{{- else -}}
{{- printf "false" }}
{{- end -}}
{{- end -}}

Using the template

Inside another template

When using template inside golang template syntax, you will need to escape them with round brackets:

{{- define "flagUsage" -}}
{{- if eq (include "isFlagEnabled" .) "true" -}}
{{- printf "%s" (include "isFlagEnabled" .) -}}
{{- end -}}
{{- end -}}

another example used inside a resource

Pay attention the template is being used twice in the example, once as an operand for the if operator and one as text for the label

{{- if eq (include "isFlagEnabled" .) "true" -}} {{/* <--- operand used in spring function surrounded by `{{ }}` */}}
apiVersion: v1
kind: Service
metadata:
    name: {{ include "my-chart.fullname" . }}
    labels:
        my-meta-label: {{ include "isFlagEnabled" . }} {{/* <---- plain text */}}
spec:
    type: {{ .Values.service.type }}
    ports:
        - port: {{ .Values.service.port }}
        targetPort: http
        protocol: TCP
        name: http
    selector:
        {{- include "my-chart.selectorLabels" . | nindent 4 }}
{{- end }}

Answer 2

To build on @Totem's excellent and helpful answer, you can make the "isFlagEnabled" template reusable across multiple flags.

{{- define "isFlagEnabled" -}}
{{- $root := index . "root" -}}
{{- $flag := index . "flag" -}}
{{- if (index $root.Values $root.Chart.Name) -}}
{{- if hasKey (index $root.Values $root.Chart.Name) $flag -}}
{{- (index (index $root.Values $root.Chart.Name) $flag).enabled -}}
{{- end -}}
{{- else if hasKey $root.Values $flag -}}
{{- (index $root.Values $flag).enabled -}}
{{- else -}}
{{- printf "false" }}
{{- end -}}
{{- end -}}

Use it in the yaml file like so:

{{- if eq (include "isFlagEnabled" (dict "root" . "flag" "myflag")) "true" }}

Local values file:

myflag:
  enabled: false

Overriding values file:

mychart:
  myflag:
    enabled: true

This worked for me in the situation where I had a subchart that needed to be overridden by a global chart, and I wanted to reference the chart by name in the global chart.