github-actions-runner-aws

About

This repository contains the Dockerfile for a self-hosted GitHub Actions runner and an associated Terraform module which can be run in your environment to provision:

• ECS Cluster
• ECS Service
• ECS Fargate task definition to spin up an instance of this runner per job in your GitHub Actions workflow

This module uses an existing ECR repository in AWS, and so does not provision one.

Set Up

1. Create and request access for a Github robot user.
   • Create EUA account for robot user
   • Create Github account for robot user
   • Request permission for the robot user within Github
   • Create an access token for the robot user within Github
   • Store the access token in AWS Secrets Manager
     • The secret's name must start with github-runner due to IAM restrictions on the ecs-task-role
2. Set up an IAM user in AWS with the necessary permissions to support the docker-build.yml workflow script included. See IAM User Permissions section below for details.
   • Once you have your user, be sure to add the access key details to your repository's Secrets
3. Provision the Terraform module in this repository.
4. You should now be able to push images to the org level ECR repository via a push to your main branch or a new release. An ECS Cluster and Service should be set up for you.
5. See the documentation on usage of the runner on how to deploy runners to your service.

IAM User Permissions

Creation of the IAM user, group, and attached policy should be submitted via CMS Jira to the Cloud Support team.

For the IAM user needed for Github to interact with AWS (specifically ECR and ECS):

• the username should be github-runner
• the user should be a part of the group github-runner-group
• the permissions policy (github-runners) should be attached to the group to follow best practices

In the IAM policy, the following variables should be updated to be the appropriate account ID and region for your deployment:

• $AWS_ACCOUNT_ID
• $AWS_REGION

All of the specified resources in the IAM policy do not have to exist prior to the policy being created.

github-runners IAM policy:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "IAMActions",
            "Effect": "Allow",
            "Action": [
                "iam:GetRole",
                "iam:PassRole"
            ],
            "Resource": "arn:aws:iam::$AWS_ACCOUNT_ID:role/ecs-task-role-*"
        },
        {
            "Sid": "ECRTokenAndECSTaskActions",
            "Effect": "Allow",
            "Action": [
                "ecs:RegisterTaskDefinition",
                "ecr:GetAuthorizationToken",
                "ecs:DescribeTaskDefinition"
            ],
            "Resource": "*"
        },
        {
            "Sid": "ECSClusterActions",
            "Effect": "Allow",
            "Action": [
                "ecs:DescribeServices",
                "ecs:UpdateService"
            ],
            "Resource": [
                "arn:aws:ecs:$AWS_REGION:$AWS_ACCOUNT_ID:cluster/gh-runner-*",
                "arn:aws:ecs:$AWS_REGION:$AWS_ACCOUNT_ID:service/gh-runner-*"
            ]
        }
    ]
}

NOTE: Including a path to IAM roles

Should you decide to populate the optional path variable in this module, ensure that the Resource the iam:GetRole and PassRole are enabled on includes the path you specify. e.g. "arn:aws:iam::$AWS_ACCOUNT_ID:role/path/you/specified/ecs-task-role-*"

Local Github Token Testing

This is strictly for testing purposes. These steps help test a Github token by running the docker image and enabling you to manually trigger the entrypoint.sh script locally via Docker. This does not require any AWS infrastructure deployed.

The entrypoint.sh script is what sets-up the docker image to act as a runner, including registration with the repository specified.

1. Clone this repository to your machine.
2. Ensure your environment variables are populated:
   • PERSONAL_ACCESS_TOKEN - Your github personal access token with repository permissions.
     • Go to Settings > Developer Settings > Personal Access Token, and click on Generate new token
     • Give your token a note and check the box to give full control of private repositories
     • Once generated, be sure to save your token in a secure location such as 1pass or AWS Secrets Manager
   • REPO_OWNER - The name of the repository owner, e.g. CMSgov
   • REPO_NAME - The name of the repository you are configuring the runners for
3. Build and run the image. ./entrypoint.sh should register the runner with your repository and start listening for jobs.
4. In one of the workflows in the target repository, change the runs-on value to self-hosted. This will make the workflow use the registered self-hosted runner to complete its task, after which it will shut down.

Terraform Module

This repository contains a Terraform module to deploy an ECS cluster, ECS service, and log to Cloudwatch in support of automating deployment of ephemeral self-hosted Github Actions runners within AWS.

This module supports the following features:

• Optionally pass an existing ECS Cluster, and if not, create one
• Set default desired count for ECS Service (default is 0, assuming it will be managed by Github Actions workflow)

Usage

module "github-actions-runner-aws" {
  source = "github.com/cmsgov/github-actions-runner-aws?ref=v2.0.0"

  # ECS variables
  environment               = "${environment}"
  ecs_vpc_id                = "${vpc.id}"
  ecs_subnet_ids            = "${vpc.private_subnets.id}"

  # GitHub Runner variables
  personal_access_token_arn = "${secretsmanager.token.arn}"
  github_repo_name          = "${repo_name}"
}

Data Sources

Some existing variable information can be looked-up in AWS via data sources. For example:

data "aws_secretsmanager_secret_version" "token" {
  secret_id = "/github-runner-dev/token"
}

Will let you then use the ARN of that data source in this way:

personal_access_token_arn = data.aws_secretsmanager_secret_version.token.arn

Required Parameters

Name	Description
environment	Environment name (used in naming resources)
ecs_vpc_id	VPC ID to be used by ECS
ecs_subnet_ids	Subnet IDs for the ECS tasks.
personal_access_token_arn	AWS SecretsManager ARN for GitHub personal access token
github_repo_name	The Github repository name

Optional Parameters

Name	Default Value	Description
cloudwatch_log_retention	731	Number of days to retain Cloudwatch logs
ecr_repo_tag	"latest"	The tag to identify and pull the image in ECR repo
ecs_desired_count	0	Sets the default desired count for task definitions within the ECS service
assign_public_ip	"false"	Choose whether to assign a public IP address to the Elastic Network Interface
role_path	"/"	The path in which to create the assume roles and policies. Refer to the AWS docs for more
permissions_boundary	""	ARN of the policy that is used to set the permissions boundary for the role
github_repo_owner	"CMSgov"	The name of the Github repo owner.
tags	{}	Additional tags to apply

Outputs

None.

Requirements

Name	Version
terraform	>= 0.13
aws	>= 3.0

Modules

None.