Terraform import ECS task definition from another project - amazon-web-services

Question

I have multiple projects, each with their own Terraform to manage the AWS infrastructure specific to that project. Infrastructure that's shared (a VPC for example): I import into the projects that need it.
I want to glue together a number of different tasks from across different services using step functions, but some of them are Fargate ECS tasks. This means I need to specify the task definition ARN in the step function.
I can import a task definition but if I later update the project that manages that task definition, the revision will change while the step function will continue to point at the old task definition revision.
At this point I might as well hard-code the task ARN into the step function and just have to remember to update it in the future.
Anyone know a way around this?

Answer 1

You can use the aws_ecs_task_definition data source to look up the latest revision of a task definition family:
data "aws_ecs_task_definition" "example" {
task_definition = "example"
}
output "example" {
value = data.aws_ecs_task_definition.example
}
Applying this gives the following output (assuming you have an example service in your AWS account):
example = {
"family" = "example"
"id" = "arn:aws:ecs:eu-west-1:1234567890:task-definition/example:333"
"network_mode" = "bridge"
"revision" = 333
"status" = "ACTIVE"
"task_definition" = "example"
"task_role_arn" = "arn:aws:iam::1234567890:role/example"
}
So you could do something like this:
data "aws_ecs_task_definition" "example" {
task_definition = "example"
}
data "aws_ecs_cluster" "example" {
cluster_name = "example"
}
resource "aws_sfn_state_machine" "sfn_state_machine" {
name = "my-state-machine"
role_arn = aws_iam_role.iam_for_sfn.arn
definition = <<EOF
{
"StartAt": "Manage ECS task",
"States": {
"Manage ECS task": {
"Type": "Task",
"Resource": "arn:aws:states:::ecs:runTask.waitForTaskToken",
"Parameters": {
"LaunchType": "FARGATE",
"Cluster": ${data.aws_ecs_cluster.example.arn},
"TaskDefinition": ${data.aws_ecs_task_definition.example.id},
"Overrides": {
"ContainerOverrides": [
{
"Name": "example",
"Environment": [
{
"Name": "TASK_TOKEN_ENV_VARIABLE",
"Value.$": "$$.Task.Token"
}
]
}
]
}
},
"End": true
}
}
}
EOF
}