Ensure SECRET information is not included in container definition for AWS ECS service

Including SECRET information in container definition may cause sensitive information disclosure.

For Amazon ECS best practices, see the AWS documentation (below).

In Terraform -

1. In the aws_ecs_task_definition resource, set the container_definitions field appropriately.
2. If sensitive information is required, pass this data to containers as environment variables.

References:
https://docs.aws.amazon.com/AmazonECS/latest/developerguide/Welcome.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ecs_task_definition