How to manage automatic deployment to ECS using Terraform Cloud and CircleCI?

Question

I have an ECS task which has 2 containers using 2 different images, both hosted in ECR. There are 2 GitHub repos for the two images (app and api), and a third repo for my IaC code (infra). I am managing my AWS infrastructure using Terraform Cloud. The ECS task definition is defined there using Cloudposse's ecs-alb-service-task, with the containers defined using ecs-container-definition. Presently I'm using latest as the image tag in the task definition defined in Terraform.

I am using CircleCI to build the Docker containers when I push changes to GitHub. I am tagging each image with latest and the variable ${CIRCLE_SHA1}. Both repos also update the task definition using the aws-ecs orb's deploy-service-update job, setting the tag used by each container image to the SHA1 (not latest). Example:

          container-image-name-updates: "container=api,tag=${CIRCLE_SHA1}"

When I push code to the repo for e.g. api, a new version of the task definition is created, the service's version is updated, and the existing task is restarted using the new version. So far so good.

The problem is that when I update the infrastructure with Terraform, the service isn't behaving as I would expect. The ecs-alb-service-task has a boolean called ignore_changes_task_definition, which is true by default.

• When I leave it as true, Terraform Cloud successfully creates a new version whenever I Apply changes to the task definition. (A recent example was to update environment variables.) BUT it doesn't update the version used by the service, so the service carries on using the old version. Even if I stop a task, it will respawn using the old version. I have to manually go in and use the Update flow, or push changes to one of the code repos. Then CircleCI will create yet aother version of the task definition and update the service.

• If I instead set this to false, Terraform Cloud will undo the changes to the service performed by CircleCI. It will reset the task definition version to the last version it created itself!

So I have three questions:

1. How can I get Terraform to play nice with the task definitions created by CircleCI, while also updating the service itself if I ever change it via Terraform?

2. Is it a problem to be making changes to the task definition from THREE different places?

3. Is it a problem that the image tag is latest in Terraform (because I don't know what the SHA1 is)?

I'd really appreciate some guidance on how to properly set up this CI flow. I have found next to nothing online about how to use Terraform Cloud with CI products.

Answer 1

I have learned a bit more about this problem. It seems like the right solution is to use a CircleCI workflow to manage Terraform Cloud, instead of having the two services effectively competing with each other. By default Terraform Cloud will expect you to link a repo with it and it will auto-plan every time you push. But you can turn that off and use the terraform orb instead to run plan/apply via CircleCI.

You would still leave ignore_changes_task_definition set to true. Instead, you'd add another step to the workflow after the terraform/apply step has made the change. This would be aws-ecs/run-task, which should relaunch the service using the most recent task definition, which was (possibly) just created by the previous step. (See the task-definition parameter.)

I have decided that this isn't worth the effort for me, at least not at this time. The conflict between Terraform Cloud and CircleCI is annoying, but isn't that acute.