ECS container instance draining on lifecycle events

Overview

Automates Container Instance Draining in Amazon ECS by removing tasks from an instance before scaling down a cluster with Auto Scaling Groups. Heavily inspired by this blog post from AWS. Lambda source code taken from and terraform inspired by the CloudFormation stack from Amazon available here.

It works by consuming lifecyle events from an autoscaling group. When an autoscaling:EC2_INSTANCE_TERMINATING event happens for the specified ASG it is placed on an SNS topic which in turn triggers lambda that will drain the tasks first from the ECS instance and then terminate the instance once the number of tasks on the instance become zero.

Usage

data "aws_region" "current" {}

module "example_module_test" {
  source = "git::https://github.com/edispark/terraform-ecs-container-instance-draining"

  autoscaling_group_name = "arn:partition:service:region:account-id:autoScalingGroupName/XXX"
  autoscaling_group_arn = "my-asg-name"
  ecs_cluster_arn = "arn:partition:service:region:account-id:cluster/XXX"
  ecs_cluster_name = "my-ecs-cluster-name"

  region                 = data.aws_region.current.name
}

Requirements

Name	Version
terraform	>= 0.12.26
aws	>= 3.0
local	1.4.0

Providers

Name	Version
aws	>= 3.0
local	1.4.0

Inputs

Name	Description	Type	Default	Required
autoscaling_group_arn	The name of the Auto Scaling group to which you want to assign the lifecycle hook to	string	n/a	yes
autoscaling_group_name	The name of the Auto Scaling group to which you want to assign the lifecycle hook to	string	n/a	yes
ecs_cluster_arn	Specifies the ECS Cluster ARN with which the resources would be associated	string	n/a	yes
ecs_cluster_name	Specifies the ECS Cluster Name with which the resources would be associated	string	n/a	yes
region	AWS Region for ECS cluster	string	n/a	yes
tags	Additional tags (_e.g._ { BusinessUnit : ABC })	map(string)	{}	no

Outputs

Name	Description
sns_topic_arn	Topic used by ASG to send notifications when instance state is changing

Development

Prerequisites

• terraform
• terraform-docs
• pre-commit
• golang
• golint

Configurations

• Configure pre-commit hooks

pre-commit install

• Configure golang deps for tests

> go get github.com/gruntwork-io/terratest/modules/terraform
> go get github.com/stretchr/testify/assert

Tests

• Tests are available in test directory
• In the test directory, run the below command

go test