feat(chart): allow to run tpl on ServiceAccount annotations

[fcrespofastly]

Description

The basic use-case is to add dynamic environmental metadata to external-dns KSA so we can take advantage of advanced cloud IAM features such as IRSA or Workload Identity. We already provide the necessary metadata through values so we could DRY those values and render them in values files. For instance:

serviceAccount:
  annotations:
    iam.gke.io/gcp-service-account: "external-dns@{{ .Values.metadata.gcpProject }}.iam.gserviceaccount"

This change doesn't break any previous behavior.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: fcrespofastly / name: Fernando Crespo Grávalos (5126e3a, 8114c5c, 6754d80, a336198, 85eaee9, c88c6dc, 0a3cbfd)

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[fcrespofastly]

Hey @szuecs @stevehipwell 👋🏻 !

How do you feel about this change? it should be basically noop, can we launch the tests?

[fcrespofastly]

I also updated the CHANGELOG adding an entry under UNRELEASED.

@szuecs @stevehipwell ☝🏻 I think that's correct right?

[mloiseleur]

/ok-to-test
/lgtm
/retitle feat(chart): allow to run tpl on ServiceAccount annotations

[mloiseleur]

/assign @stevehipwell
/unassign @szuecs

[ivankatliarchuk]

Is it not safer to create a helper function in _helpers.tpl, and reference it in template?

{{- define "external-dns.serviceAccountAnnotations" -}}
...

Then for example if someone deploy external-dns with umbrella chart can override behaviour in local _helpers.tpl?

Example

apiVersion: v2
name: external-dns-umbrella
dependencies:
- name: external-dns
  version: 1.15.0
  repository: https://kubernetes-sigs.github.io/external-dns/

and in my local _helper.tpl

{{- define "external-dns.serviceAccountAnnotations" -}}
.. behaviour override

[fcrespofastly]

Hey @ivankatliarchuk 👋🏻 !

Thanks for suggesting this, that's an interesting approach as well! I don't mind iterating on this towards your suggested approach, but I want to make sure we're all on the same page:

• By running tpl() we're not changing the behaviour, right? We're just allowing to treat a string as a template. Is there any use case where this change breaks template rendering that I'm missing?
• If we do this with service account annotations, then should we do it with podAnnotations too just to be consistent? If the answer is yes, then the scope of this PR will be bigger I guess.
• What would be the default template when the local helper is not defined?

@stevehipwell thoughts?

Thanks folks!

[stevehipwell]

Thanks for the PR @fcrespofastly but the implementation isn't correct due to the way helm works with YAML blobs. This can be solved with a loop as the annotations are a fixed simple type.

Please could you also update the comment in values.yaml so the ability to template is added to the docs (you need to run helm-docs after making this change to update README.md).

[stevehipwell]

Suggested change

	{{- tpl (toYaml .) $ | nindent 4 }}
	{{- range $k, $v := . }}
	{{- printf "%s: %s" (tpl $k $) (tpl $v $) }}
	{{- end }}

[stevehipwell]

Suggested change

	- Allow templatizing `serviceaccount.annotations` in values, by rendering them using `tpl` built-in function: [#4958](https://github.com/kubernetes-sigs/external-dns/pull/4958) @fcrespofastly
	- Allow templating `serviceaccount.annotations` keys and values, by rendering them using the `tpl` built-in function. ([#4958](https://github.com/kubernetes-sigs/external-dns/pull/4958)) _@fcrespofastly_

[fcrespofastly]

@stevehipwell thanks for the feedback!! I implemented the suggested changes, plus a minor nit (nindent).

Out of curiosity now, why the initial implementation doesn't work exactly? You mentioned due to the way Helm handles YAML blobs but I was wondering if you could provide with an example (again, just curiosity)

Thanks again!

[stevehipwell]

Suggested change

	# -- Annotations to add to the service account. Templates are allowed here. Example:
	# annotations:
	# example.com/annotation: {{ .Values.nameOverride }}
	# -- Annotations to add to the service account. Templates are allowed in both the key and value; for example `example.com/annotation/{{ .Values.nameOverride }}: {{ .Values.nameOverride }}`.

Helm docs doesn't support multi-line strings.

[fcrespofastly]

Done! thanks!

[stevehipwell]

Thanks @fcrespofastly. Could you add a templated annotation to the charts/external-dns/ci/ci-values.yaml file so this pattern is validated?

[fcrespofastly]

@stevehipwell done! 🚀

[stevehipwell]

/label tide/merge-method-squash
/lgtm
/approve

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