Convert yaml to property file in helm template

Question

I would like to convert a part of the structure in values.yaml to properties file in a config map.

Is it possible to convert a yaml structure like:

field1: value1
field2:
   field21: value21
   field22: value22

into

field1=value1
field2.field21=value21
field2.field22=value22

with Helm templating functions?

Answer 1

As a programming problem, this is a straightforward recursive call. You can use Go text/template templates like functions. The one trick here is that they only take a single parameter, so you need to use the sprig list function to pack multiple values into that parameter, and the text/template index function to get values back out.

{{- define "envify" -}}
{{- $prefix := index . 0 -}}
{{- $value := index . 1 -}}
{{- if kindIs "map" $value -}}
  {{- range $k, $v := $value -}}
    {{- template "envify" (list (printf "%s.%s" $prefix $k) $v) -}}
  {{- end -}}
{{- else -}}
{{ $prefix }}={{ $value }}
{{ end -}}

data:
{{ template "envify" (list "" .Values.fields) | indent 2 }}

This will work with arbitrarily deep nested values.

If you refer to standard Helm variables (.Release, .Values, ...) this also becomes tricky because the . variable is reused for the single template parameter (it also gets reused within the range loop). I tend to explicitly pass it as an additional template parameter.

{{- $top := index . 2 -}}
# from the {{ $top.Chart.Name }} Helm chart

{{/* in your ConfigMap proper */}}
{{ template "envify" (list "" .Values.fields .) }}