Allow template rendering in Cluster managed services value

[willj-ti]

I want to be able to dynamically name additional services. I am working towards deploying a Cluster that is externally visible through a LoadBalancer Service, and I want this additional service to have a dynamic name.

In this section from (cluster.yaml)[https://github.com/cloudnative-pg/charts/blob/main/charts/cluster/templates/cluster.yaml#L105], the config is populated as literals, without template rendering.

  {{- if not (and (empty .Values.cluster.roles) (empty .Values.cluster.services)) }}
  managed:
    {{- with .Values.cluster.services }}
    services:
      {{- toYaml . | nindent 6 }}
    {{ end }}
    {{- with .Values.cluster.roles }}
    roles:
      {{- toYaml . | nindent 6 }}
    {{ end }}
  {{- end }}

I'm fairly new to Helm, but my first idea is to add a tpl function to wrap the value somewhere in this block, e.g. {{- toYaml (tpl .) | nindent 6 }}

This is what I'm expecting my own values.yaml to look like:

cluster:
  services:
    additional:
      - selectorType: rw
        serviceTemplate:
          metadata:
            name: '{{ $.Release.Name }}-pg'
          spec:
            type: LoadBalancer
        updateStrategy: patch

Note the templated value is a string, to be evaluated later by tpl.

I am definitely open for feedback on this, including any other way to accomplish this, any pitfalls with tpl, or even a telling off that I'm doing Helm or CNPG all wrong. In the meantime, I'll fork and try it out.

[dosubot]

Hi @willj-ti! I'm Dosu and I’m helping the charts team.

You're on the right track—using Helm's tpl function is a common way to enable dynamic naming for resources like services. The current CloudNativePG Helm chart renders managed services using toYaml, which means any templated strings in your values (like {{ $.Release.Name }}-pg) won't be evaluated unless you modify the chart to wrap those values with tpl during rendering. This change is not present in the official chart yet, but there is an open pull request proposing exactly this enhancement for fields like cluster.services and serviceTemplate source.

If you fork the chart, you can update the relevant block in cluster.yaml to something like:

{{- range .Values.cluster.services.additional }}
  - selectorType: {{ .selectorType }}
    serviceTemplate:
      {{- tpl (toYaml .serviceTemplate) $ | nindent 6 }}
    updateStrategy: {{ .updateStrategy | default "patch" }}
{{- end }}

This will allow you to use Helm template expressions in your values.yaml, and they'll be evaluated at install time.

Pitfalls and best practices:

• Only string values are evaluated by tpl, so complex objects need careful handling.
• Avoid evaluating untrusted user input with tpl—it can introduce security risks if not managed with proper RBAC discussion.
• Make sure your service names don't clash with reserved names like <CLUSTER_NAME>-<SERVICE_NAME> docs.

This approach is widely used for dynamic resource naming in Helm, but always test thoroughly to avoid surprises in production.

To reply, just mention @dosu.

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[willj-ti]

The bot's right, there is already a PR for this (from 3 hours ago, wow!). Closing as completed, optimistic about the PR.