Ensure public repositories are disabled for Amazon Elastic Container Registry (Amazon ECR)

Allowing unrestricted, public access to cloud services could open an application up to external attack. Disallowing this access is typically considered best practice.

In AWS Console -

1. Sign in to the AWS Console and go to the Amazon ECR console.
2. Select Repositories.
3. Click the image repository that you want to configure. Select Permissions.
4. In the Permission statements, select the policy statement.
5. Click Edit and make the necessary changes.

In Terraform -

1. In the aws_ecr_repository_policy resource, set the policy accordingly.
   To learn more about how to write an IAM policy, see the AWS documentation.

References:
https://docs.aws.amazon.com/AmazonECR/latest/userguide/security-iam.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ecr_repository_policy