Helm Charts with multiple lists in multiple values files

Question

I have a values.yaml that has the following:

abc:
  env:
  - name: name01
    value: value01
  - name: name02
    value: value02

and I have another values file values-dev.yaml that I add when installing using -f and it has:

abc:
  env:
  - name: name03
    value: value03

and using range I list them in my template. My hope was that the list would become like this after both files are applied:

abc:
  env:
  - name: name01
    value: value01
  - name: name02
    value: value02
  - name: name03
    value: value03

but the values-dev.yaml values will override the one in the values.yaml and it becomes:

abc:
  env:
  - name: name03
    value: value03

How can I achieve merging these 2 lists with the same field names from different values files?

Answer 1

Short answer is, you can not merge lists.

In your case abc.env is the key and the value is a list. Let me re-write your first values file in an equivalent notation and it will be more clear:

abc:
  env: [{name: name01, value: value01}, {name: name02, value: value02}]

So Helm is doing what is expected, overriding the key abc.env with the last provided one.

Solution is re-structuring your values files, like this:

abc:
  env:
    name01: value01
    name02: value02

This way, you can merge and override your values files as desired. This way, it's also much easy to override a single value with command line flag, for example:

--set abc.env.name01=different

With some Helm magic, it's easy to pass those values as environment variables to your pods:

...
  containers:
  - name: abc
    image: abc
    env:
    {{- range $key, $value := .Values.abc.env }}
    - name: {{ $key }}
      value: {{ $value | quote }}
    {{- end }}