How can I connect my autoscaling group to my ecs cluster?

Question

In all tutorials for ECS you need to create a cluster and after that an autoscaling group, that will spawn instances. Somehow in all these tutorials the instances magically show

Answer 1

I was struggling with this for a while. The key to getting the instances in the autoscaling group associated with your ECS cluster is in the user data. When you are creating your launch config when you get to step 3 "Configure Details" hit the advanced tab and enter a simple bash script like the following for your user data.

#!/usr/bin/env bash
echo ECS_CLUSTER=your_cluster_name >> /etc/ecs/ecs.config

All the available parameters for agent configuration can be found here http://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-agent-config.html

Answer 2

An autoscaling group is not strictly associated to a cluster. However, an autoscaling group can be configured such that each instance launched registers itself into a particular cluster.

Registering an instance into a cluster is the responsibility of the ECS Agent running on the instance. If you're using the Amazon ECS-optimized AMI, the ECS Agent will launch when the instance boots and register itself into the configured cluster. However, you can also use the ECS Agent on other Linux AMIs by following the installation instructions.

Answer 3

Well, i found out. Its all about the ecs-agent and its config file /etc/ecs/ecs.config (This file will be created through the Userdata field, when creating EC2 instances, even from an autoscaling configuration.) Read about its configuration options here: http://docs.aws.amazon.com/AmazonECS/latest/developerguide/ecs-agent-config.html

But you can even copy a ecs.config stored on Amazon S3, do it like this (following lines go into Userdata field):

#!/bin/bash
yum install -y aws-cli
aws configure set default.s3.signature_version s3v4
aws configure set default.s3.addressing_style path
aws configure set default.region eu-central-1
aws s3 cp s3://<bucketname>/ecs.config /etc/ecs/ecs.config

note: Signature_version v4 is specific for some regions, like eu-central-1. This ofc only works, if your IAM role for the instance (in my case its ecsInstanceRole) has the right AmazonS3ReadOnlyAccess

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The AWS GUI console way for that would be: Use the cluster wizard at https://console.aws.amazon.com/ecs/home#/firstRun . It will create an autoscaling grou for your cluster, a loadbalancer in front of it, and connect it all nicely.