Terraform dynamic block - amazon-ecs

Question

I'm having trouble creating a dynamic block in Terraform. I'm trying to create an ECS service using a module. In the module I want to specify that network_configuration block should be created only if a variable is present.
Here's my module code:
resource "aws_ecs_service" "service" {
name = var.name
cluster = var.cluster
task_definition = var.task_definition
desired_count = var.desired_count
launch_type = var.launch_type
load_balancer {
target_group_arn = var.lb_target_group
container_name = var.container_name
container_port = var.container_port
}
dynamic "network_configuration" {
for_each = var.network_config
content {
subnets = network_configuration.value["subnets"]
security_groups = network_configuration.value["security_groups"]
assign_public_ip = network_configuration.value["public_ip"]
}
}
}
Next is code for the actual service:
module "fargate_service" {
source = "./modules/ecs/service"
name = "fargate-service"
cluster = module.ecs_cluster.id
task_definition = module.fargate_task_definition.arn
desired_count = 2
launch_type = "FARGATE"
lb_target_group = module.target_group.arn
container_name = "fargate_definition"
container_port = 8000
network_config = local.fargate_network_config
}
Finally my locals file looks like this:
locals {
fargate_network_config = {
subnets = module.ec2_vpc.private_subnet_ids
public_ip = "false"
security_groups = [module.fargate_sg.id]
}
}
With the above configuration I wish to create one network_configiration block only when network_config variable is present. If I don't define it I want the module not to bother creating the block.
I'm getting Invalid index error.
network_configuration.value is tuple with 3 elements
The given key does not identify an element in this collection value: a number
is required.
What is wrong with my code? This is my first time using dynamic blocks in Terraform but I want to be able to understand it.
Thanks

Answer 1

So your locals should be as follows:
locals {
fargate_network_config = [
{
subnets = module.ec2_vpc.private_subnet_ids
public_ip = "false"
security_groups = [module.fargate_sg.id]
}
]
}
Then fix your variable network_config to be a list.
Finally your dynamic block:
dynamic "network_configuration" {
for_each = var.network_config
content {
subnets = lookup(network_configuration.value, "subnets", null)
security_groups = lookup(network_configuration.value, "security_groups", null)
assign_public_ip = lookup(network_configuration.value, "public_ip", null)
}
}
hope that helps