Supports toggling eks auto mode on and off

The API has a number of constraints that make this a litle difficult,
but it does work.

1.  The node_role_arn cannot be changed without recreating the cluster.
    This is an API limitation, not a terraform provider bug.
    https://docs.aws.amazon.com/eks/latest/APIReference/API_ComputeConfigRequest.html

2.  If node_pools is not empty, then the node_role_arn *must* be provided.

3.  If the node_role_arn is provided, then node_pools must not be empty!

If you enable Auto Mode and set node_pools to a non-empty value, which requires
setting node_role_arn, you cannot later change node_pools to an empty value,
unless you also unset the node_role_arn. But if you unset the node_role_arn,
then the cluster will be recreated due to the first point above.

So, we *can* support disabling auto-mode without recreating a cluster, but only
if node_pools is not empty and if node_role_arn does not change.

Fixes terraform-aws-modules#3273

Author: lorengordon

examples/eks-auto-mode/main.tf

@@ -38,6 +38,10 @@ module "eks" {
 
   enable_cluster_creator_admin_permissions = true
 
+  # Set `bootstrap_self_managed_addons` to false to support disabling auto mode,
+  # without recreating the cluster
+  bootstrap_self_managed_addons = false
+
   cluster_compute_config = {
     enabled    = true
     node_pools = ["general-purpose"]

main.tf

@@ -57,8 +57,8 @@ resource "aws_eks_cluster" "this" {
 
     content {
       enabled       = local.auto_mode_enabled
-      node_pools    = local.auto_mode_enabled ? try(compute_config.value.node_pools, []) : null
-      node_role_arn = local.auto_mode_enabled && length(try(compute_config.value.node_pools, [])) > 0 ? try(compute_config.value.node_role_arn, aws_iam_role.eks_auto[0].arn, null) : null
+      node_pools    = try(compute_config.value.node_pools, [])
+      node_role_arn = length(try(compute_config.value.node_pools, [])) > 0 ? try(compute_config.value.node_role_arn, aws_iam_role.eks_auto[0].arn, null) : null
     }
   }
 
@@ -848,7 +848,7 @@ resource "aws_eks_identity_provider_config" "this" {
 ################################################################################
 
 locals {
-  create_node_iam_role = local.create && var.create_node_iam_role && local.auto_mode_enabled
+  create_node_iam_role = local.create && var.create_node_iam_role
   node_iam_role_name   = coalesce(var.node_iam_role_name, "${var.cluster_name}-eks-auto")
 }