aws: Switch EC2 instances to use resource-based hostnames

* Use EC2 resource-based hostnames instead of IP-based hostnames. The Amazon
DNS server can resolve A and AAAA queries to IPv4 and IPv6 node addresses
* For example, nodes used to be named like `ip-10-11-12-13.us-east-1.compute.internal`
but going forward use the instance id `i-0123456789abcdef.us-east-1.compute.internal`
* Tag controller node EBS volumes with a name based on the controller node name

aws/flatcar-linux/kubernetes/controllers.tf

@@ -20,11 +20,8 @@ resource "aws_instance" "controllers" {
   tags = {
     Name = "${var.cluster_name}-controller-${count.index}"
   }
-
   instance_type = var.controller_type
-
-  ami       = local.ami_id
-  user_data = data.ct_config.controllers.*.rendered[count.index]
+  ami           = local.ami_id
 
   # storage
   root_block_device {
@@ -32,7 +29,9 @@ resource "aws_instance" "controllers" {
     volume_size = var.controller_disk_size
     iops        = var.controller_disk_iops
     encrypted   = true
-    tags        = {}
+    tags = {
+      Name = "${var.cluster_name}-controller-${count.index}"
+    }
   }
 
   # network
@@ -40,6 +39,10 @@ resource "aws_instance" "controllers" {
   subnet_id                   = element(aws_subnet.public.*.id, count.index)
   vpc_security_group_ids      = [aws_security_group.controller.id]
 
+  # boot
+  user_data = data.ct_config.controllers.*.rendered[count.index]
+
+  # cost
   credit_specification {
     cpu_credits = var.controller_cpu_credits
   }

aws/flatcar-linux/kubernetes/network.tf

@@ -47,17 +47,25 @@ resource "aws_route" "egress-ipv6" {
 resource "aws_subnet" "public" {
   count = length(data.aws_availability_zones.all.names)
 
-  vpc_id            = aws_vpc.network.id
-  availability_zone = data.aws_availability_zones.all.names[count.index]
-
-  cidr_block                      = cidrsubnet(var.host_cidr, 4, count.index)
-  ipv6_cidr_block                 = cidrsubnet(aws_vpc.network.ipv6_cidr_block, 8, count.index)
-  map_public_ip_on_launch         = true
-  assign_ipv6_address_on_creation = true
-
   tags = {
     "Name" = "${var.cluster_name}-public-${count.index}"
   }
+  vpc_id            = aws_vpc.network.id
+  availability_zone = data.aws_availability_zones.all.names[count.index]
+
+  # IPv4 and IPv6 CIDR blocks
+  cidr_block      = cidrsubnet(var.host_cidr, 4, count.index)
+  ipv6_cidr_block = cidrsubnet(aws_vpc.network.ipv6_cidr_block, 8, count.index)
+
+  # Assign IPv4 and IPv6 addresses to instances
+  map_public_ip_on_launch         = true
+  assign_ipv6_address_on_creation = true
+
+  # Hostnames assigned to instances
+  # resource-name: <ec2-instance-id>.region.compute.internal
+  private_dns_hostname_type_on_launch            = "resource-name"
+  enable_resource_name_dns_a_record_on_launch    = true
+  enable_resource_name_dns_aaaa_record_on_launch = true
 }
 
 resource "aws_route_table_association" "public" {

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

@@ -3,16 +3,14 @@ resource "aws_autoscaling_group" "workers" {
   name = "${var.name}-worker"
 
   # count
-  desired_capacity          = var.worker_count
-  min_size                  = var.worker_count
-  max_size                  = var.worker_count + 2
-  default_cooldown          = 30
-  health_check_grace_period = 30
+  desired_capacity = var.worker_count
+  min_size         = var.worker_count
+  max_size         = var.worker_count + 2
 
   # network
   vpc_zone_identifier = var.subnet_ids
 
-  # template
+  # instance template
   launch_template {
     id      = aws_launch_template.worker.id
     version = aws_launch_template.worker.latest_version
@@ -32,6 +30,10 @@ resource "aws_autoscaling_group" "workers" {
       min_healthy_percentage = 90
     }
   }
+  # Grace period before checking new instance's health
+  health_check_grace_period = 30
+  # Cooldown period between scaling activities
+  default_cooldown = 30
 
   lifecycle {
     # override the default destroy and replace update behavior
@@ -60,8 +62,6 @@ resource "aws_launch_template" "worker" {
     enabled = false
   }
 
-  user_data = sensitive(base64encode(data.ct_config.worker.rendered))
-
   # storage
   ebs_optimized = true
   block_device_mappings {
@@ -76,7 +76,13 @@ resource "aws_launch_template" "worker" {
   }
 
   # network
-  vpc_security_group_ids = var.security_groups
+  network_interfaces {
+    associate_public_ip_address = true
+    security_groups             = var.security_groups
+  }
+
+  # boot
+  user_data = sensitive(base64encode(data.ct_config.worker.rendered))
 
   # metadata
   metadata_options {