Finding the values for executionRoleArn, taskRoleArn

Question

I'm working through an AWS Python tutorial, module 2.

I'm at the point Section C, where I have to create a task definition by filling in some REPLACE_ME values in a json file.

{
  "family": "mythicalmysfitsservice",
  "cpu": "256",
  "memory": "512",
  "networkMode": "awsvpc",
  "requiresCompatibilities": [
    "FARGATE"
  ],
  "executionRoleArn": "REPLACE_ME_ECS_SERVICE_ROLE_ARN",
  "taskRoleArn": "REPLACE_ME_ECS_TASK_ROLE_ARN",
  "containerDefinitions": [
    {
      "name": "MythicalMysfits-Service",
      "image": "REPLACE_ME_IMAGE_TAG_USED_IN_ECR_PUSH",
      "portMappings": [
        {
          "containerPort": 8080,
          "protocol": "http"
        }
      ],
      "logConfiguration": {
        "logDriver": "awslogs",
        "options": {
          "awslogs-group": "mythicalmysfits-logs",
          "awslogs-region": "us-east-1",
          "awslogs-stream-prefix": "awslogs-mythicalmysfits-service"
        }
      },
      "essential": true
    }
  ]
}

There are three variables I'm not sure where to get the values:

"REPLACE_ME_ECS_SERVICE_ROLE_ARN", 
"REPLACE_ME_ECS_TASK_ROLE_ARN", 
"REPLACE_ME_IMAGE_TAG_USED_IN_ECR_PUSH"

Before this step, in steps A and B, I create-cluster, but the output of that doesn't indicate obvious values to me:

$ aws ecs create-cluster --cluster-name MythicalMysfits-Cluster
{
    "cluster": {
        "clusterArn": "arn:aws:ecs:us-east-1:002847010850:cluster/MythicalMysfits-Cluster",
        "clusterName": "MythicalMysfits-Cluster",
        "status": "ACTIVE",
        "registeredContainerInstancesCount": 0,
        "runningTasksCount": 0,
        "pendingTasksCount": 0,
        "activeServicesCount": 0,
        "statistics": [],
        "tags": [],
        "settings": [
            {
                "name": "containerInsights",
                "value": "disabled"
            }
        ],
        "capacityProviders": [],
        "defaultCapacityProviderStrategy": []
    }
}

The only value I suspect I might know is, "REPLACE_ME_IMAGE_TAG_USED_IN_ECR_PUSH" which i could take from docker push 002847010850.dkr.ecr.us-east-1.amazonaws.com/mythicalmysfits/service when I pushed a docker image to the Elastic Compute Repository

So I made a guess and used the "clusterArn" value for both REPLACE_ME's, and the original image tag for the third but

$ aws ecs register-task-definition --cli-input-json file://~/environment/aws-modern-application-workshop/module-2/aws-cli/task-definition.json

An error occurred (ClientException) when calling the RegisterTaskDefinition operation: Role is not valid

This is the json I fed it:

{
  "family": "mythicalmysfitsservice",
  "cpu": "256",
  "memory": "512",
  "networkMode": "awsvpc",
  "requiresCompatibilities": [
    "FARGATE"
  ],
  "executionRoleArn": "arn:aws:ecs:us-east-1:002847010850:cluster/MythicalMysfits-Cluster",
  "taskRoleArn": "arn:aws:ecs:us-east-1:002847010850:cluster/MythicalMysfits-Cluster",
  "containerDefinitions": [
    {
      "name": "MythicalMysfits-Service",
      "image": "002847010850.dkr.ecr.us-east-1.amazonaws.com/mythicalmysfits/service",
      "portMappings": [
        {
          "containerPort": 8080,
          "protocol": "http"
        }
      ],
      "logConfiguration": {
        "logDriver": "awslogs",
        "options": {
          "awslogs-group": "mythicalmysfits-logs",
          "awslogs-region": "us-east-1",
          "awslogs-stream-prefix": "awslogs-mythicalmysfits-service"
        }
      },
      "essential": true
    }
  ]
}

Can anyone advise where I'm going wrong here? This tutorial is pretty lousy -- just a bunch of incantations, very brittle, and no obvious forum discussions to work through it.

Answer 1

Marcin's suggestion of an answer caused me to to rethink and look at a JSON output from earlier in the tutorial.

aws cloudformation describe-stacks --stack-name MythicalMysfitsCoreStack gives a pile of key/value pairs and both REPLACE_ME_ECS_SERVICE_ROLE_ARN REPLACE_ME_ECS_TASK_ROLE_ARN OutputValues are inside there.

Then the procedure works.