feat: Option to pass kubeVersion to helm template

[msvticket]

To be able to use helmfile template to render helm charts for cluster with other than the default Kubernetes version in helm you might need to add the --kube-version flag to helm. This adds that functionality.

[44smkn]

Hi,

I found Datadog Chart use .Capabilities.KubeVersion.GitVersion.
https://github.com/DataDog/helm-charts/blob/de93d7c45467c2bf65a34afec0729f13341aed4f/charts/datadog/templates/_helpers.tpl#L521-L526

{{- define "enable-service-internal-traffic-policy" -}}
{{- if or (semverCompare "^1.22-0" .Capabilities.KubeVersion.GitVersion) .Values.agents.localService.forceLocalServiceEnabled -}}
true
{{- else -}}
false
{{- end -}}
{{- end -}}

If enable-service-internal-traffic-policy is true, the kind: Service resource manifest which contains internalTrafficPolicy will be generated.
internalTrafficPolicy feature can be used only on Kubernetes 1.22+.
The clusters we have are v1.19 and v1.21, so we're a little troubled.

This pull request may resolve our problem.
I would like to know the status of this.

[msvticket]

The reason I need this feature myself is that I need to set pathType in the ingresses for prometheus. But the prometheus chart only allows setting the pathType in Kubernetes 1.19+

https://github.com/prometheus-community/helm-charts/blob/main/charts/prometheus/templates/_helpers.tpl#L200

[msvticket]

What can I do to get this pull request merged?

[mumoshu]

I'm still unsure this is the right level to where kubeVersion is defined, as Helmfile allows a different k8s cluster hence k8s version per release, by specifying releases[].kubecontext. But I do believe this is a good enough for a starter!

[mumoshu]

LGTM. Thanks for your patience and contribution!

[mumoshu]

@msvticket @44smkn Hey! I recently learned that --kube-version is only present in helm2's helm template. So if your chart is relying solely on Capabilities.KubeVersion to detect the correct API version for a resource, this doesn't help.

But you're already using Helm 3, right? Then you should just list API versions available to helm template by specifying apiVersions in your helmfile.yaml.

[mumoshu]

Updated README to note the above info 91aa0ac

[msvticket]

$ helm template --help | grep kube-version
--kube-version string Kubernetes version used for Capabilities.KubeVersion
$ helm version
version.BuildInfo{Version:"v3.6.3", GitCommit:"d506314abfb5d21419df8c7e7e68012379db2354", GitTreeState:"dirty", GoVersion:"go1.16.5"}

--kube-version was added again in version 3.6.0 with helm/helm#9040

[44smkn]

When I ran helmfile template using helm v3.7.2 and helmfile v0.143.0, I got the expected results.
I think the feature proposed in this PR is useful in helm3 as well.

[mumoshu]

@msvticket @44smkn Good to know! Thank you so much for sharing ☺️