google_container_cluster: Add support for initialClusterVersion

[safaci2000]

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Description

When creating a GKE cluster the version of the master node is set via the initialClusterVersion as can be seen detailed in the API spec here: https://cloud.google.com/kubernetes-engine/docs/reference/rest/v1beta1/projects.locations.clusters

string

The initial Kubernetes version for this cluster. Valid versions are those found in validMasterVersions returned by getServerConfig. The version can be upgraded over time; such upgrades are reflected in currentMasterVersion and currentNodeVersion.

Users may specify either explicit versions offered by Kubernetes Engine or version aliases, which have the following behavior:

"latest": picks the highest valid Kubernetes version
"1.X": picks the highest valid patch+gke.N patch in the 1.X version
"1.X.Y": picks the highest valid gke.N patch in the 1.X.Y version
"1.X.Y-gke.N": picks an explicit Kubernetes version
"","-": picks the default Kubernetes version

I saw an older ticket that asks for a similar request listed here but I'm not sure if the feature did not exist then or I'm not understanding something. If this feature already exists please let me know.

New or Affected Resource(s)

• google_container_cluster

Potential Terraform Configuration

NA

References

https://cloud.google.com/kubernetes-engine/docs/reference/rest/v1beta1/projects.locations.clusters

b/392629415

[rileykarson]

This is supported as https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/container_cluster#min_master_version-1, which maps to cluster version update mechanics as well

We could probably add support for a separate initial field that was never used for updates, but it would be very prone to recreating the resource because changes would imply a recreation so that that was the initial version of the cluster.