ECS Deployment fails when using EXTERNAL launch type Task

Issue

Users automating Amazon Elastic Container Services (ECS) cannot deploy and may see errors from Clouddriver. The logs may indicate caching cycle failures when a Service in the ECS account with deployment type EXTERNAL is defined with taskSets, and Spinnaker retrieves an empty TaskDefinitionArn, which doesn’t ignore and tries to describe it continuously and causes this failure: 'com.amazonaws.services.ecs.model.InvalidParameterException: Task Definition can not be blank. (Service: AmazonECS; Status Code: 400; Error Code: InvalidParameterException; Request ID: fcf39ec3-0e98-48f3-bb40-8b6ab19a7be5; Proxy: null)'  

Cause

There's a reported** issue** in OSS Spinnaker where the ECS provider causes the caching agent to fail when an ACTIVE service is defined with an EXTERNAL launch type. The error occurs when calling a task definition** because there is no task definition **but uses the taskSet field.  This is the sample service definition:

{
    "services": [
        {
            "serviceArn": "arn:aws:ecs:us-east-1:xxxxxxxxxxxx:service/test-cluster/test",
            "serviceName": "test",
            "clusterArn": "arn:aws:ecs:us-east-1:xxxxxxxxxxxx:cluster/test-cluster",
            "loadBalancers": [],
            "serviceRegistries": [],
            "status": "ACTIVE",
            "desiredCount": 1,
            "runningCount": 0,
            "pendingCount": 0,
            "launchType": "EC2",
            "deploymentConfiguration": {
                "maximumPercent": 200,
                "minimumHealthyPercent": 100
            },
            "taskSets": [],
            "deployments": [],
            "roleArn": "arn:aws:iam::xxxxxxxxxxxx:role/aws-service-role/ecs.amazonaws.com/AWSServiceRoleForECS",
            "events": [],
            "createdAt": 1640098677.085,
            "placementConstraints": [],
            "placementStrategy": [],
            "schedulingStrategy": "REPLICA",
            "deploymentController": {
                "type": "EXTERNAL"
            },
            "createdBy": "arn:aws:iam::xxxxxxxxxxxx:role/admin",
            "enableECSManagedTags": false,
            "propagateTags": "NONE",
            "enableExecuteCommand": false
        }
    ],
    "failures": []
}