How to overwrite Table/Mapping in Helm Chart

Question

I have a values.yaml that has

ingress:
  enabled: false 

volume:
  hostPath:
    path: /tmp
    type: DirectoryOrCreate 

I have an overlay.yaml that changes the value of values.yaml.

ingress:
  enabled: true 

volume:
  persistentVolumeClaim:
    claimName: test

For the ingress, it's working as I suspected because the value of enabled will change to true. However, for the volume, it appears that tables add on to each other rather than get overwritten. For instance, I would get something like:

volume: 
  persistentVolumeClaim:
    claimName: test
  hostPath:
    path: /tmp
    type: DirectoryOrCreate 

I would like to specify a default volume type and its configurations (e.g. path) in values.yaml, but have the freedom for others to change this through an overlay. However, what I have now "adds" a volume type rather than overwrite it. Is there a way to accomplish this?

Answer 1

null is a specific valid YAML value (the same as JSON null). If you set a Helm value to null, then the Go text/template logic will unmarshal it to Go nil and it will appear as "false" in if statements and similar conditionals.

volume:
  persistentVolumeClaim:
    claimName: test
  hostPath: null

I might avoid this problem in chart logic, though. One approach would be to use a separate type field to say which sub-field you're looking for:

# the chart's defaults in values.yaml
volume:
  type: HostPath
  hostPath: { ... }

# your `helm install -f` overrides
volume:
  type: PersistentVolumeClaim
  persistentVolumeClaim: { ... }
  # (the default hostPath: will be present but unused)

A second option is to make the default "absent", and either disable the feature entirely or construct sensible defaults in the chart code if it's not present.

# values.yaml

# volume specifies where the application will keep persistent data.
# If unset, each replica will have independent data and this data will
# be lost on restart.
#
# volume:
#
#  persistentVolumeClaim stores data in an existing PVC.
#
#  persistentVolumeClaim:
#    name: ???

# deep in templates/deployment.yaml
volumes:
{{- if .Values.volume.persistentVolumeClaim }}
  - name: storage
    persistentVolumeClaim:
      claimName: {{ .Values.volume.persistentVolumeClaim.name }}
{{- else if .Values.volume.hostPath }}
  - name: storage
    hostPath:
      path: {{ .Values.volume.hostPath.path }}
{{- end }}
{{-/* (just don't create a volume if not set) */}}

Or, to always provide some kind of storage, even if it's not that useful:

volumes:
  - name: storage
{{- if .Values.volume.persistentVolumeClaim }}
    persistentVolumeClaim:
      claimName: {{ .Values.volume.persistentVolumeClaim.name }}
{{- else if .Values.volume.hostPath }}
    hostPath:
      path: {{ .Values.volume.hostPath.path }}
{{- else }}
    emptyDir: {}
{{- end }}