AWS ECS Deploy Service by Template Action

A github action, that updates a service with a new image based on an existing task definition.

Usage

      - name: deploy to ECS
        uses: modum-io/aws-ecs-deploy-service-by-template@v1.0.0
        with:
          image: "modumio/sample@${{ steps.docker_build.outputs.digest }}"
          template-task-definition: sample_template
          container-name: sample
          target-task-definition: sample
          cluster: app
          service: sample

See action.yml for the full documentation for this action's inputs and outputs.

Credentials

This action relies on the default behavior of the AWS SDK for Javascript to determine AWS credentials and region.

Terraform

This action can be useful if you use Terraform to manage your task definition and don't want terraform changes to trigger a new deployment. For this you can set up a 'blueprint' template task definition and service in Terraform like this:

resource "aws_ecs_task_definition" "sample" {
  family                   = "sample_template"
  [...]

  container_definitions    = <<TASK_DEFINITION
  [ 
    { 
      "name": "sample", 
      "image": "nginx",
      "portMappings": [ { "containerPort": 80 } ],
      "repositoryCredentials": {
      "environment": [ { "name": "SOME_ENV", "value": "some value" } ]
    }
  ]
  TASK_DEFINITION
}

resource "aws_ecs_service" "sample" {
  name            = "sample"
  [...]
  task_definition = aws_ecs_task_definition.sample.arn

  lifecycle {
    ignore_changes = [task_definition]
  }
}

On first deployment the service will be launched with the sample_template task definition. However your github action step would for each deploy make a copy of sample_template, change the image field, register it under the name sample and then update the service to use the new task definition. This separates configuration from deployment, keeps your Terraform plan "clean" and prevents accidental rollbacks, if you forget to update the image in terraform.