aws_ecr_repository: add newest_image_tag for improving experience with tag immutability

[francardoso93]

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Description

data.aws_ecr_repository.service could have the tag of the newest pushed image as an attribute. That would grant a dynamic experience when working with immutable tags.

See this example that works fine when dealing with mutable tags:

resource "aws_lambda_function" "lambda_function" {
  package_type  = "Image"
  image_uri  = "${data.aws_ecr_repository.service.repository_url}:${var.image_version}"
  ...
}

Now, if I can't set image_version to latest, how to make sure terraform apply will keep up to date with newest image? To keep updating the image_version value manually seems like unnecessary work and poor experience.

Tag immutability should be used in production for hardening security, a better experience in doing so could drive that change in many systems.

New or Affected Resource(s)

aws_ecr_repository

Potential Terraform Configuration

resource "aws_lambda_function" "lambda_function" {
  package_type  = "Image"
  image_uri        = "${data.aws_ecr_repository.service.repository_url}:${data.aws_ecr_repository.service.newest_image_tag}"
  ...
}

or even better:

resource "aws_lambda_function" "lambda_function" {
  package_type  = "Image"
  image_uri        = "${data.aws_ecr_repository.service.newest_image_uri}"
  ...
}

References

https://sysdig.com/blog/toctou-tag-mutability/
https://aquasecurity.github.io/tfsec/v1.15.0/checks/aws/ecr/enforce-immutable-repository/

[anitakrueger]

We are running into exactly this issue with a Fargate task definition. The definition is in terraform and originally creates the resource with the latest image tag. A github workflow then updates the task definition when a new image gets deployed. The workflow does move the latest tag as well, but it also creates a specific version on release, which is what I want to set my image in the task definition to. Now running terraform again, overwrites that and I have no way of querying what the latest image is.

[iRevive]

I have a similar issue. I use Terraform to provision the resources (ECS, EC2, etc). But deployments are managed by the GitLab pipeline: the script updates the task definition with a new tag.

To prevent Terraform from reverting the tag, I ignore changes in the task definition:

resource "aws_ecs_service" "service" {
  ...
  lifecycle {
    ignore_changes = [task_definition, desired_count]
  }
}

This approach works fine until something apart from the image tag needs to be changed in the task definition (e.g. add a new environment variable).

[github-actions]

This functionality has been released in v4.56.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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