Master and Node Versions Default to Latest

[trotttrotttrott]

This is as opposed to letting GKE figure out the latest patch suffix. This strategy does not work for specifying node version - only masters. An explicit patch suffix is required for node version.

Latest, "...specifies the highest supported Kubernetes version currently available on GKE in the cluster's zone or region" 1. I've tested this in us-west1, us-west2, and us-central1 and it's worked as suspected - all masters and nodes were launched with version 1.11.2-gke.18.

An alternate approach would be to use the google_container_engine_versions data source. This would be useful if we had a need to target a specific minor or patch version as the default. I would argue that it's more appropriate for the projects that use this module to utilize google_container_engine_versions to satisfy project-specific needs.

[morgante]

An alternate approach would be to use the google_container_engine_versions data source.

I think this is a better option, as it will at least make the Terraform version declarative.

[trotttrotttrott]

@morgante my mistake, this data source is already in use: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/blob/master/main.tf#L31-L32. While a specific version is not declared in the module code, the value of the latest_node_version attribute is passed in to the GKE API on launch. Unless we'd like to make the default an older version for some reason, latest seems to me to be the way to go here.

I did spend some time thinking about how we could implement logic around an explicit version like 1.10.6. Theoretically, we could search the valid_node_versions attribute, but Terraform does not support filtering lists by regex. Nothing particularly elegant comes to mind. I suspect the solution would add more complexity than value.

[morgante]

Got it, LGTM.