Enable optional custom AMI's

variables.tf

+variable "ami_id" {
+  description = "Custom AMI ID for the EKS cluster; defaults to latest Amazon-provided AMI if empty"
+  default     = ""
+}
+
 variable "cluster_name" {
   description = "Name for the EKS cluster"
 }

workers.tf

@@ -2,7 +2,7 @@ resource "aws_launch_configuration" "workers" {
   associate_public_ip_address = false
   ebs_optimized               = "${var.ebs_optimized_workers}"
   iam_instance_profile        = "${aws_iam_instance_profile.workers.name}"
-  image_id                    = "${data.aws_ami.eks_worker.id}"
+  image_id                    = "${var.ami_id != "" ? var.ami_id : data.aws_ami.eks_worker.id}"
   instance_type               = "${var.instance_type}"
   name_prefix                 = "${var.cluster_name}-eks-workers-"
   security_groups             = ["${aws_security_group.workers.id}"]