Nodes are created across the given subnets.

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" {