Add support for worker pools on AWS

* Allow groups of workers to be defined and joined to
a cluster (i.e. worker pools)
* Move worker resources into a Terraform submodule
* Output variables needed for passing to worker pools
* Add usage docs for AWS worker pools (advanced)

aws/container-linux/kubernetes/workers/workers.tf

@@ -0,0 +1,74 @@
+# Workers AutoScaling Group
+resource "aws_autoscaling_group" "workers" {
+  name = "${var.cluster_name}-worker ${aws_launch_configuration.worker.name}"
+
+  # count
+  desired_capacity          = "${var.count}"
+  min_size                  = "${var.count}"
+  max_size                  = "${var.count + 2}"
+  default_cooldown          = 30
+  health_check_grace_period = 30
+
+  # network
+  vpc_zone_identifier = ["${var.subnet_ids}"]
+
+  # template
+  launch_configuration = "${aws_launch_configuration.worker.name}"
+
+  # target groups to which instances should be added
+  target_group_arns = [
+    "${aws_lb_target_group.workers-http.id}",
+    "${aws_lb_target_group.workers-https.id}",
+  ]
+
+  lifecycle {
+    # override the default destroy and replace update behavior
+    create_before_destroy = true
+    ignore_changes        = ["image_id"]
+  }
+
+  tags = [{
+    key                 = "Name"
+    value               = "${var.cluster_name}-worker"
+    propagate_at_launch = true
+  }]
+}
+
+# Worker template
+resource "aws_launch_configuration" "worker" {
+  image_id      = "${data.aws_ami.coreos.image_id}"
+  instance_type = "${var.instance_type}"
+
+  user_data = "${data.ct_config.worker_ign.rendered}"
+
+  # storage
+  root_block_device {
+    volume_type = "standard"
+    volume_size = "${var.disk_size}"
+  }
+
+  # network
+  security_groups = ["${var.security_groups}"]
+
+  lifecycle {
+    // Override the default destroy and replace update behavior
+    create_before_destroy = true
+  }
+}
+
+# Worker Container Linux Config
+data "template_file" "worker_config" {
+  template = "${file("${path.module}/cl/worker.yaml.tmpl")}"
+
+  vars = {
+    kubeconfig            = "${indent(10, var.kubeconfig)}"
+    ssh_authorized_key    = "${var.ssh_authorized_key}"
+    k8s_dns_service_ip    = "${cidrhost(var.service_cidr, 10)}"
+    cluster_domain_suffix = "${var.cluster_domain_suffix}"
+  }
+}
+
+data "ct_config" "worker_ign" {
+  content      = "${data.template_file.worker_config.rendered}"
+  pretty_print = false
+}