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kuberneteskubernetes-helmgo-templates

Usage of variables in Helm

I'm using a Helm chart and I was wondering how I can define a value by default. In my case, I wanna define a date when it isn't defined in values.yaml and I have the following code:

{{- if ne .Value.persistence.home.restoreBackup.date "" }}
{{- $bkDate := .Value.persistence.home.restoreBackup.date }}
{{- else }}
{{- $bkDate := "2022-01-01" }}
{{- end }}

I wanna set $bkDate to an specific date if it is not defined in .Value.persistence.home.restoreBackup.date but when I try to print $bkDate it is empty.

Do you know what is wrong here?

Solution

  • The Go text/template documentation notes (under "Variables"):

    A variable's scope extends to the "end" action of the control structure ("if", "with", or "range") in which it is declared....

    This essentially means you can't define a variable inside an if block and have it visible outside the block.

    For what you want to do, the Helm default function provides a straightforward workaround. You can unconditionally define the variable, but its value is the Helm value or else some default if that's not defined.

    {{- $bkDate := .Value.persistence.home.restoreBackup.date | default "2022-01-01" -}}

    (Note that a couple of things other than empty-string are "false" for purposes of default, including "unset", nil, and empty-list, but practically this won't matter to you.)

    If you need more complex logic than this then the ternary function could meet your needs {{- $var := $someCondition | ternary "trueValue" "falseValue" -}} but this leads to hard-to-read expressions, and it might be better to refactor to avoid this.