How to Create AWS Task Definition JSON from Existing task definition?

Question

I have a an existing task definition 'my-task-definition' that I can get the data for using 'aws ecs describe-task-definition --task-definition my-task-definition' (I put the output of that into my_file.json'). But my understanding is that the output from 'aws ecs describe-task-definition --task-definition my-task-definition' is not valid input for 'aws ecs register-task-definition --cli-input-json file://<path_to_json_file>/my_file.json'. What additional piece(s) of data do I have to add to that file (or remove from it). The file (with the arns changed) is below:

{
    "taskDefinition": {
        "taskDefinitionArn": "arn:aws:ecs:us-west-1:112233445566:task-definition/my-task-definition:64",
        "containerDefinitions": [
            {
                "name": "my-container",
                "image": "123456789023.dkr.ecr.us-west-1.amazonaws.com/monolith-repo:latest",
                "cpu": 0,
                "memory": 1600,
                "portMappings": [
                    {
                        "containerPort": 8080,
                        "hostPort": 0,
                        "protocol": "tcp"
                    }
                ],
                "essential": true,
                "environment": [
                    {
                        "name": "SERVER_FLAVOR",
                        "value": "JOB"
                    }
                ],
                "mountPoints": [],
                "volumesFrom": [],
                "linuxParameters": {
                    "initProcessEnabled": true
                },
                "logConfiguration": {
                    "logDriver": "awslogs",
                    "options": {
                        "awslogs-group": "/ecs/my-task-definition",
                        "awslogs-region": "us-west-1",
                        "awslogs-stream-prefix": "ecs"
                    }
                }
            }
        ],
        "family": "my-task-definition",
        "taskRoleArn": "arn:aws:iam::111222333444:role/my_role",
        "networkMode": "bridge",
        "revision": 64,
        "volumes": [],
        "status": "ACTIVE",
        "requiresAttributes": [
            {
                "name": "com.amazonaws.ecs.capability.logging-driver.awslogs"
            },
            {
                "name": "com.amazonaws.ecs.capability.ecr-auth"
            },
            {
                "name": "com.amazonaws.ecs.capability.docker-remote-api.1.19"
            },
            {
                "name": "com.amazonaws.ecs.capability.task-iam-role"
            },
            {
                "name": "com.amazonaws.ecs.capability.docker-remote-api.1.25"
            }
        ],
        "placementConstraints": [],
        "compatibilities": [
            "EXTERNAL",
            "EC2"
        ],
        "requiresCompatibilities": [
            "EC2"
        ]
    }
}

Answer 1

You are getting an error because the output from the aws ecs describe-task-definition command has additional fields that are not recognized by the aws ecs register-task-definition command.

There is no built in solution to be able to easily update a running Task Definition using the AWS CLI. However, it is possible to script a solution using a tool like jq.

One possible solution is something like this:

TASK_DEFINITION=$(aws ecs describe-task-definition --task-definition "$TASK_FAMILY" --region "us-east-1")
NEW_TASK_DEFINTIION=$(echo $TASK_DEFINITION | jq --arg IMAGE "$NEW_IMAGE" '.taskDefinition | .containerDefinitions[0].image = $IMAGE | del(.taskDefinitionArn) | del(.revision) | del(.status) | del(.requiresAttributes) | del(.compatibilities)')
aws ecs register-task-definition --region "us-east-1" --cli-input-json "$NEW_TASK_DEFINITION"

These commands update the docker image in an existing task definition and delete the extra fields so that you can register a new task definition.

There is an open Github Issue that is tracking this issue. https://github.com/aws/aws-cli/issues/3064