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Distribute workload between ECS tasks

If your ECS tasks are receiving traffic from a load balancer then the workload will be equally distributed between them. How about when we are using ECS tasks as a worker farm to handle long running jobs? And say, we want some workers to work on some partitions of the data but not all of them? Then each ECS task must know their identity and the number of tasks that belong to the same service as well.

1. Get task ARN

With ${ECS_CONTAINER_METADATA_URI_V4}/task endpoint, we can get the task ARN and metadata about its cluster and family. The docs are here.

After sending a GET request from our container, we got:

    "Cluster": "default",
    "TaskARN": "arn:aws:ecs:us-west-2:111122223333:task/default/158d1c8083dd49d6b527399fd6414f5c",
    "Family": "curltest",

This request doesn’t require any authentication at all, as long as we send it from our ECS task.

2. List all tasks in the same service

With Cluster and Family of a task, we can list all running tasks in a service using ECS API, in this example we will use Go SDK though:

list := ecsClient.ListTasks(context.TODO(), &ecs.ListTasksInput{
	Cluster:       "default",
	Family:        "curltest",
	DesiredStatus: types.DesiredStatusRunning,

list.TaskArns contains all ARN of tasks in the service, including the task making the request. This request does require authentication nevertheless.

3. Distribute the workload

Now we know how many tasks we got, the problem becomes easy.

Written on August 19, 2021.