docs: Re-add 'Tags for the ASG to support cluster-autoscaler scale up from 0' example (#2494)

Co-authored-by: Bryant Biggs <bryantbiggs@gmail.com>

examples/eks_managed_node_group/README.md

@@ -53,6 +53,7 @@ Note that this example may create resources which cost money. Run `terraform des
 
 | Name | Type |
 |------|------|
+| [aws_autoscaling_group_tag.cluster_autoscaler_label_tags](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/autoscaling_group_tag) | resource |
 | [aws_iam_policy.node_additional](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/iam_policy) | resource |
 | [aws_security_group.remote_access](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/security_group) | resource |
 | [aws_ami.eks_default](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/ami) | data source |

examples/eks_managed_node_group/main.tf

@@ -462,3 +462,52 @@ data "aws_ami" "eks_default_bottlerocket" {
     values = ["bottlerocket-aws-k8s-${local.cluster_version}-x86_64-*"]
   }
 }
+
+################################################################################
+# Tags for the ASG to support cluster-autoscaler scale up from 0
+################################################################################
+
+locals {
+
+  # We need to lookup K8s taint effect from the AWS API value
+  taint_effects = {
+    NO_SCHEDULE        = "NoSchedule"
+    NO_EXECUTE         = "NoExecute"
+    PREFER_NO_SCHEDULE = "PreferNoSchedule"
+  }
+
+  cluster_autoscaler_label_tags = merge([
+    for name, group in module.eks.eks_managed_node_groups : {
+      for label_name, label_value in coalesce(group.node_group_labels, {}) : "${name}|label|${label_name}" => {
+        autoscaling_group = group.node_group_autoscaling_group_names[0],
+        key               = "k8s.io/cluster-autoscaler/node-template/label/${label_name}",
+        value             = label_value,
+      }
+    }
+  ]...)
+
+  cluster_autoscaler_taint_tags = merge([
+    for name, group in module.eks.eks_managed_node_groups : {
+      for taint in coalesce(group.node_group_taints, []) : "${name}|taint|${taint.key}" => {
+        autoscaling_group = group.node_group_autoscaling_group_names[0],
+        key               = "k8s.io/cluster-autoscaler/node-template/taint/${taint.key}"
+        value             = "${taint.value}:${local.taint_effects[taint.effect]}"
+      }
+    }
+  ]...)
+
+  cluster_autoscaler_asg_tags = merge(local.cluster_autoscaler_label_tags, local.cluster_autoscaler_taint_tags)
+}
+
+resource "aws_autoscaling_group_tag" "cluster_autoscaler_label_tags" {
+  for_each = local.cluster_autoscaler_asg_tags
+
+  autoscaling_group_name = each.value.autoscaling_group
+
+  tag {
+    key   = each.value.key
+    value = each.value.value
+
+    propagate_at_launch = false
+  }
+}