Fluentd: Add the ability to template values for volumes, volumeMounts, and initContainers

[Boojapho]

Use cases

• I would like the ability to reuse values from the pod's container in initContainers without repeating them (e.g. image, pull policy, env).
• I would like the ability to mount configmap files based on iterating over files in a directory. In my case, I have added a directory containing my files and a configmap generator to create the CMs. I would like to use Helm templating to create the volumes / volumeMounts instead of hand jamming the names into a values file.

Current

The helm template performs a toYaml for volumes, volumeMounts, and initcontainers. This restricts these items to literal values only.

Proposal

Use tpl to allow the values to be either literal or a Helm template. Example:

{{- with .Values.volumeMounts -}}
{{- tpl (ternary . (toYaml .) (kindIs "string" .)) $ | trim | nindent 4 -}}
{{- end -}}

This would allow literals...

volumeMounts:
- name: myvol
  mountPath: /tmp/myvol

arrays with Helm...

volumeMounts:
- name: {{ include "fluentd.myvol.name" . }}
  mountPath: /tmp/myvol

or a Helm template string...

volumeMounts: |-
  {{- range $path, $_ := $.Files.Glob "myfiles/*.conf" -}}
  - name: {{ include "fluend.myvol.name" (base $path) }}
    mountPath: /tmp/myvol
  {{ end -}}

Other

This technique could be extended to other values in the future if a use case is presented