fix: include zero value local_ssd_ephemeral_storage_count for GKE nodepool disktype=hyperdisk-balanced…

[shlomimn]

Preview

I recently tried to create a new nodepool with machine_type=c4-highcpu-4 using a disk_type=hyperdisk-balanced
My GCP managed cluster controlplane version=1.32.8-gke.1134000
I am using terraform to add the new GKE nodepool.

Since my nodepool uses disk_type=hyperdisk-balanced (and not disk_type=pd-ssd),
the GKE API always assumes that the node pool might want ephemeral storage (since this is typically chosen for high-performance workloads), so it always exposes ephemeralStorageLocalSsdConfig: {} even if local_ssd_count = 0.

Problem

Following the preview above, the API wants to add ephemeralStorageLocalSsdConfig: {} when creating a new nodepool with disk_type=hyperdisk-balanced but then the GKE code checks whether local_ssd_count exists.
Since local_ssd_count doesn't exist in my nodepool configuration then terraform wants to omit ephemeralStorageLocalSsdConfig: {}

Relevant Code in cluster.tf

https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/blob/main/modules/beta-private-cluster/cluster.tf
dynamic "ephemeral_storage_local_ssd_config" { for_each = **lookup(each.value, "local_ssd_ephemeral_storage_count", 0) > 0** || lookup(each.value, "ephemeral_storage_local_ssd_data_cache_count", 0) > 0 ? [1] : [] content { local_ssd_count = lookup(each.value, "local_ssd_ephemeral_storage_count", 0) data_cache_count = lookup(each.value, "ephemeral_storage_local_ssd_data_cache_count", 0) } }

FInal Result

Finally the terraform codes shows: Plan: 1 to add, 0 to change, 1 to destroy.

`# module.gke.google_container_cluster.primary has changed ~ resource "google_container_cluster" "primary" {
...
...

• ephemeral_storage_local_ssd_config { + local_ssd_count = 0 }
  ...
  ...
  Terraform will perform the following actions: # module.gke.google_container_node_pool.pools["event-proc"] must be replaced -/+ resource "google_container_node_pool" "pools" {
  ...
  ...

• ephemeral_storage_local_ssd_config { # forces replacement - local_ssd_count = 0 -> null }
• ...
• ...
• Plan: 1 to add, 0 to change, 1 to destroy.`

Suggested Solution

If add the option in the code not to remove dynamic "ephemeral_storage_local_ssd_config"
In case local_ssd_count=0 this will align with the API exposes ephemeralStorageLocalSsdConfig: {} even if local_ssd_count=0

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[gemini-code-assist]

Summary of Changes

Hello @shlomimn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where Terraform would incorrectly attempt to replace GKE nodepools configured with hyperdisk-balanced disk types. The GKE API expects the ephemeralStorageLocalSsdConfig block to always be present for these nodepools, even if no local SSDs are specified (i.e., local_ssd_count is zero). Previously, Terraform's configuration only included this block if local_ssd_ephemeral_storage_count was greater than zero, leading to a discrepancy and unnecessary resource recreation. The change updates the conditional logic to include the configuration block when the count is zero or greater, ensuring proper alignment with the GKE API and preventing unwanted nodepool replacements.

Highlights

• GKE Nodepool Configuration: Modified the condition for including ephemeral_storage_local_ssd_config in GKE nodepool configurations to allow for zero local_ssd_ephemeral_storage_count when using hyperdisk-balanced disk types, aligning with GKE API expectations.

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[gemini-code-assist]

Code Review

This pull request aims to fix an issue where Terraform produces a perpetual diff for GKE node pools using hyperdisk-balanced disk type, because the GKE API expects the ephemeralStorageLocalSsdConfig block even with zero counts. While the intent is correct, the implementation has a couple of issues. First, the change is made to a generated file (modules/beta-public-cluster/cluster.tf) and should be applied to the source template (autogen/main/cluster.tf.tmpl) to be effective and persistent. Second, the proposed logic >= 0 is too broad and will add the ephemeral_storage_local_ssd_config block to all node pools, which could cause issues for configurations that do not support it. I've suggested a more targeted fix that applies the logic only when necessary. It would also be beneficial to add an integration test to cover this new scenario.

[gemini-code-assist]

This change should be applied to the template file autogen/main/cluster.tf.tmpl instead of this generated file. Otherwise, it will be overwritten.

Additionally, the condition lookup(each.value, "local_ssd_ephemeral_storage_count", 0) >= 0 is too broad. Since lookup with a default value of 0 will always return a number greater than or equal to zero, this will cause the ephemeral_storage_local_ssd_config block to be created for all node pools, which may have unintended consequences for node pools that do not support this configuration.

Based on your description, the issue is specific to disk_type = "hyperdisk-balanced". A safer approach is to add this specific case to the condition, preserving the original logic for other cases.

      for_each = lookup(each.value, "local_ssd_ephemeral_storage_count", 0) > 0 || lookup(each.value, "ephemeral_storage_local_ssd_data_cache_count", 0) > 0 || lookup(each.value, "disk_type", "pd-standard") == "hyperdisk-balanced" ? [1] : []

[shlomimn]

I moved the change to https://github.com//terraform-google-modules/terraform-google-kubernetes-engine/blob/main/modules/beta-private-cluster/cluster.tf

[shlomimn]

Regarding the suggested answer,
Since we are dealing with ssd and since it is suggested my solution is too broad,
the I think we can add the following change instead:

dynamic "ephemeral_storage_local_ssd_config" {
for_each = lookup(each.value, "local_ssd_ephemeral_storage_count", 0) > 0 || lookup(each.value, "ephemeral_storage_local_ssd_data_cache_count", 0) || lookup(each.value, "disk_type", "pd-ssd") == "hyperdisk-balanced" > 0 ? [1] : []
content {
local_ssd_count = lookup(each.value, "local_ssd_ephemeral_storage_count", 0)
data_cache_count = lookup(each.value, "ephemeral_storage_local_ssd_data_cache_count", 0)
}
}