If condition checking value returned by helm template

3
votes

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?

1
kubernetes-helm

1 Answers

7
votes

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 -}}
{{- end -}}
{{- else -}}
{{- printf "false" }}
{{- 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 }}