Nodes are created across the given subnets.

main.tf

@@ -1,24 +1,32 @@
 
 locals {
+  k8s-subnets-ids = [
+    module.aws-network-existing.subnet-by-name["subnet_1"].id,
+    module.aws-network-existing.subnet-by-name["subnet_3"].id,
+  ]
   nodes-config = {
     "k8s-master" = {
       base-image = var.ubuntu-ami
       aws-ec2-type = var.t2-medium-4gib-2vcpu
-      num = 0
+      subnet-ids = local.k8s-subnets-ids
+      num = 1
     },
     "k8s-worker" = {
       base-image = var.ubuntu-ami
       aws-ec2-type = var.t2-medium-4gib-2vcpu
-      num = 0
+      subnet-ids = local.k8s-subnets-ids
+      num = 2
     },
     "ansible-test" = {
       base-image = var.ubuntu-ami
       aws-ec2-type = var.t2-micro-1gib-1vcpu
+      subnet-ids = [module.aws-network-existing.subnet-by-name["subnet_2"].id]
       num = 0
     },
     "nfs" = {
       base-image = var.ubuntu-ami
       aws-ec2-type = var.t2-micro-1gib-1vcpu
+      subnet-ids = [module.aws-network-existing.subnet-by-name["subnet_4"].id]
       num = 1
     },
   }
@@ -74,6 +82,7 @@ module "aws-network-existing" {
   source                      = "./modules/aws-network-existing"
   default-vpc-name            = var.aws-existing-vpc-name
   default-security-group-name = var.aws-existing-sg-name
+  existing-subnet-names       = var.aws-existing-subnet-names
 }
 
 ################################################################################
@@ -88,11 +97,14 @@ resource "aws_key_pair" "key" {
   }
 }
 
+# resource "aws_ebs_volume" "zfs" {
+#   availability_zone =
+
 module "nodes" {
   for_each           = local.nodes-config
   source             = "./modules/aws-nodes"
   ami                = each.value.base-image
-  subnet-id          = module.aws-network-existing.k8s-subnets-ids[0]
+  subnet-ids         = each.value.subnet-ids
   security-group-ids = [module.aws-network-existing.default-sg.id]
   user-datas         = lookup(module.cloud-init-config, each.key, null).user-datas
   num-nodes          = each.value.num

modules/aws-network-existing/main.tf

@@ -22,6 +22,14 @@ data "aws_subnet" "subnets" {
   id = each.key
 }
 
+data "aws_subnet" "subnet-by-name" {
+  for_each = toset(var.existing-subnet-names)
+  filter {
+    name   = "tag:Name"
+    values = [each.key]
+  }
+}
+
 data "aws_security_group" "default" {
   name = var.default-security-group-name
 }

modules/aws-network-existing/outputs.tf

@@ -11,11 +11,16 @@ output "subnets" {
   value = data.aws_subnet.subnets
 }
 
-output "k8s-subnets-ids" {
-  description = "An array of subnets to be used for k8s VMs. These subnets were chosen by selecting a single subnet from each availability_zone."
+output "one-subnet-per-az" {
+  description = "An array of subnets that selects 1 subnet per az."
   value = [for k,v in local.az-to-subnets : v[0]]
 }
 
+output "subnet-by-name" {
+  description = "A map of subnet name to subnet resource."
+  value = data.aws_subnet.subnet-by-name
+}
+
 output "az-to-subnets" {
   description = "A map of availability zone to array of subnets that are in thet availability zone."
   value = local.az-to-subnets

modules/aws-network-existing/variables.tf

@@ -5,3 +5,9 @@ variable "default-security-group-name" {
 variable "default-vpc-name" {
   description = "The name of the existing default VPC. This module will query AWS for a VPC with this name,"
 }
+
+variable "existing-subnet-names" {
+  description = "A list of subnet names that already exist in default-vpc-name"
+  default     = []
+  type        = list(string)
+}

modules/aws-nodes/main.tf

@@ -3,7 +3,7 @@ resource "aws_instance" "nodes" {
   instance_type               = var.ec2-instance-type
   # TODO Make this a variable.
   associate_public_ip_address = true
-  subnet_id                   = var.subnet-id
+  subnet_id = element(var.subnet-ids, count.index % length(var.subnet-ids))
   vpc_security_group_ids = var.security-group-ids
   user_data = element(var.user-datas.*.rendered, count.index)
   count                       = var.num-nodes

modules/aws-nodes/variables.tf

@@ -25,9 +25,9 @@ variable "user-datas" {
   description = "A list of cloud-init configs that get applied to their corresponding node."
 }
 
-variable "subnet-id" {
-  description = "The ID of the subnet that all the nodes will be added to."
-  type = string
+variable "subnet-ids" {
+  description = "An array of subnet ids. These subnets will be round robined as the subnet to use for each node."
+  type = list(string)
 }
 
 variable "security-group-ids" {

variables.tf

@@ -14,6 +14,12 @@ variable "aws-existing-vpc-name" {
   description = "The name of the existing VPC when using aws-network-existing."
 }
 
+variable "aws-existing-subnet-names" {
+  description = "A list of subnet names that already exist in aws-existing-vpc-name"
+  default     = []
+  type        = list(string)
+}
+
 variable "aws-region" {
   default = "us-east-1"
   description = "The AWS region to use."