Managed node groups' launch template "$Latest" version producing an infinite always-changing plan

[tal-asulin]

Description

When using managed node group and setting the launch template version to "$Latest", Terraform will always show a difference in the plan and apply changes.

The issue was first introduced in older version - v17.1.0 and got fixed on v17.1.3 but the same issue happened again #1446 in newer versions (18.21.0).

• ✋ I have searched the open/closed issues and my issue is not listed.

Versions

• Module version [Required]: 18.21.0

• Terraform & providers version:
  Terraform v1.2.0
  on darwin_amd64

• provider registry.terraform.io/hashicorp/aws v4.15.1
• provider registry.terraform.io/hashicorp/cloudinit v2.2.0
• provider registry.terraform.io/hashicorp/kubernetes v2.11.0
• provider registry.terraform.io/hashicorp/tls v3.4.0

Reproduction Code [Required]

Produced using the module' example:

module "eks" {
  source          = "terraform-aws-modules/eks/aws"
  version         = "18.21.0"
  cluster_version = "1.21"
  cluster_name    = "test_cluster"
  vpc_id          = "<VPC_ID>"
  subnet_ids      = ["<SUBNET_ID_1>","<SUBNET_ID_2>]

  eks_managed_node_group_defaults = {
    disk_size               = 50
    instance_types          = ["m6i.large", "m5.large", "m5n.large", "m5zn.large"]
    launch_template_version = "$Latest"
    tags                    = {"default_tag" = "test_tag"}
  }

  eks_managed_node_groups = {
    green = {
      min_size     = 1
      max_size     = 10
      desired_size = 1

      instance_types = ["t3.large"]
      capacity_type  = "SPOT"
    }
  }
}

Steps to reproduce the behavior:

1. Apply the plan for the first time
2. Apply the plan again (without making any changes).

Expected behavior

No changes to the launch template version and the plan itself.

Actual behavior

Launch template version will constantly change from static number to $Latest even if no change was done to the plan.

Terminal Output Screenshot(s)

Additional context

[bryantbiggs]

Remove this line:

    launch_template_version = "$Latest"

[tal-asulin]

Removing this line will truly make this behaviour disappear, but isn't it a valid value to set? for example, changing launch template metadata will bump the launch template version and will be resulted with the desired change in Terraform plan.

[bryantbiggs]

It is, but see https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/eks_node_group#version

[tal-asulin]

Understood. Thanks @bryantbiggs for the quick response.

[github-actions]

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