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ecs-host-service-scale

A Lambda function to ensure an ECS Service is set to the correct Desired Count for a One-Task-Per-Host placement value for any cluster that runs the Service.

Requirements

  • boto3 (included in AWS Lambda functions, no need for packaged deployment)
  • ECS_SERVICE_ARN environment variable
  • IAM Role/Policy access setup

Flow

UML Sequence Flow

Deployment

The function is meant to be deployed as a non-VPC Lambda function. It will probably work in a VPC environment, given an Internet Gateway and proper permissions, but it simply does not need access to any in-VPC resources, only AWS API calls.

  • IAM Policy & IAM Role allowing: ecs:Describe* and ecs:UpdateService
  • CloudWatch Event Rule for: {"source": ["aws.ecs"], "detail-type": ["ECS Container Instance State Change"]}
  • Code from lambda_function.py
  • The ECS Service ARN environment variable

Testing

  • Install all requirements via pip install -r requirements.txt
  • Execute tests vis pytest

See py.test docs and botocore Stubber reference for more.

Contributing

  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Test your changes with pytest --cov - the tests currently cover the code 100% - don't lower that number!
  4. Commit your changes (git commit -am 'Add some feature')
  5. Push to the branch (git push origin my-new-feature)
  6. Create a new Pull Request

Author

Mike Fiedler (miketheman@gmail.com)