GKE Terraformed Cluster Release Channel Setting - terraform

Question

According to THIS documentation right here I can set the release channel on a cluster. Yet it doesn't work at all. It "sees" the setting is there during the apply summary but it doesn't actually apply to a new cluster in the end. What am I missing? There are no examples given in the documentation so I'm just having to guess here. In the console I see this:
Not set, can't even set it manually:
I'm trying to set it to RAPID
release_channel {
channel = "RAPID"
}
Here's my full TF:
resource "google_container_cluster" "standard-cluster" {
enable_binary_authorization = false
enable_kubernetes_alpha = false
enable_legacy_abac = false
enable_shielded_nodes = false
initial_node_count = 0
location = local.ws_vars["zone"]
logging_service = "logging.googleapis.com/kubernetes"
monitoring_service = "monitoring.googleapis.com/kubernetes"
name = local.ws_vars["cluster-name"]
network = "projects/${local.ws_vars["project-id"]}/global/networks/${local.ws_vars["environment"]}"
project = local.ws_vars["project-id"]
subnetwork = "projects/${local.ws_vars["project-id"]}/regions/us-east4/subnetworks/${local.ws_vars["environment"]}"
release_channel {
channel = local.ws_vars["channel"]
}
ip_allocation_policy {
#cluster_ipv4_cidr_block = local.ws_vars["cidr-block"]
cluster_secondary_range_name = "subnet-pods"
services_secondary_range_name = "subnet-services"
}
addons_config {
horizontal_pod_autoscaling {
disabled = false
}
http_load_balancing {
disabled = false
}
network_policy_config {
disabled = false
}
}
database_encryption {
state = "DECRYPTED"
}
maintenance_policy {
daily_maintenance_window {
start_time = "01:00"
}
}
network_policy {
enabled = true
provider = "CALICO"
}
node_pool {
initial_node_count = 1
name = "scoped-two-cpu-high-mem-preemptible"
node_locations = [
local.ws_vars["zone"],
]
autoscaling {
max_node_count = 30
min_node_count = 0
}
management {
auto_repair = true
auto_upgrade = true
}
node_config {
disk_size_gb = 100
disk_type = "pd-standard"
guest_accelerator = []
image_type = "COS"
labels = {}
local_ssd_count = 0
machine_type = "n1-highmem-4"
metadata = {
"disable-legacy-endpoints" = "true"
workload_metadata_config = "GKE_METADATA_SERVER"
}
oauth_scopes = [
"https://www.googleapis.com/auth/devstorage.read_only",
"https://www.googleapis.com/auth/logging.write",
"https://www.googleapis.com/auth/monitoring",
"https://www.googleapis.com/auth/ndev.clouddns.readwrite",
"https://www.googleapis.com/auth/service.management.readonly",
"https://www.googleapis.com/auth/servicecontrol",
"https://www.googleapis.com/auth/trace.append",
]
preemptible = true
service_account = "default"
tags = []
taint = []
shielded_instance_config {
enable_integrity_monitoring = true
enable_secure_boot = false
}
}
upgrade_settings {
max_surge = 1
max_unavailable = 0
}
}
private_cluster_config {
enable_private_endpoint = false
enable_private_nodes = true
master_ipv4_cidr_block = "172.16.0.0/28"
}
vertical_pod_autoscaling {
enabled = true
}
workload_identity_config {
identity_namespace = "${local.ws_vars["project-id"]}.svc.id.goog"
}
}

Answer 1

I think the key is in the error message the GUI is giving you. Setting the release channel to "RAPID" today would mean to jump to GKE 1.20, which is 2 major versions newer than your cluster and this seems to be unsuported.
What happens if you set it to "STABLE" ? This is still 1.18 and shouldn't fail to set up.

Answer 2

The answer was in two parts:
The state file had a version set that was previously supported but was no longer supported. The version kept being set to this previously supported version and thus the RAPID setting couldn't take effect.
GKE requires a minimum version setting that matches one of these supported versions in order for the channel to be set correctly. This defeats the purpose of terraform and infrastructure as code since one will have to eventually change this version in the terraform in order to apply the channel. This means a drift in the TF, always. This is an obvious flaw in GKE. Ideally it should just set the version to whatever is supported.