Autoscaling with self-hosted runners

About autoscaling

You can automatically increase or decrease the number of self-hosted runners in your environment in response to the webhook events you receive with a particular label. For example, you can create automation that adds a new self-hosted runner each time you receive a workflow_job webhook event with the queued activity, which notifies you that a new job is ready for processing. The webhook payload includes label data, so you can identify the type of runner the job is requesting. Once the job has finished, you can then create automation that removes the runner in response to the workflow_job completed activity.

Supported autoscaling solutions

The actions/actions-runner-controller (ARC) project is a Kubernetes-based runner autoscaler. GitHub recommends ARC if the team deploying it has expert Kubernetes knowledge and experience.

For more information, see About Actions Runner Controller and About support for Actions Runner Controller.

Using ephemeral runners for autoscaling

GitHub recommends implementing autoscaling with ephemeral self-hosted runners; autoscaling with persistent self-hosted runners is not recommended. In certain cases, GitHub cannot guarantee that jobs are not assigned to persistent runners while they are shut down. With ephemeral runners, this can be guaranteed because GitHub only assigns one job to a runner.

This approach allows you to manage your runners as ephemeral systems, since you can use automation to provide a clean environment for each job. This helps limit the exposure of any sensitive resources from previous jobs, and also helps mitigate the risk of a compromised runner receiving new jobs.

To add an ephemeral runner to your environment, include the --ephemeral parameter when registering your runner using config.sh. For example:

./config.sh --url https://github.com/octo-org --token example-token --ephemeral

The GitHub Actions service will then automatically de-register the runner after it has processed one job. You can then create your own automation that wipes the runner after it has been de-registered.

Alternatively, you can create ephemeral, just-in-time runners using the REST API. For more information, see REST API endpoints for self-hosted runners.

Controlling runner software updates on self-hosted runners

By default, self-hosted runners will automatically perform a software update whenever a new version of the runner software is available. If you use ephemeral runners in containers then this can lead to repeated software updates when a new runner version is released. Turning off automatic updates allows you to update the runner version on the container image directly on your own schedule.

To turn off automatic software updates and install software updates yourself, specify the --disableupdate flag when registering your runner using config.sh. For example:

./config.sh --url https://github.com/YOUR-ORGANIZATION --token EXAMPLE-TOKEN --disableupdate

If you disable automatic updates, you must still update your runner version regularly. New functionality in GitHub Actions requires changes in both the GitHub Actions service and the runner software. The runner may not be able to correctly process jobs that take advantage of new features in GitHub Actions without a software update.

If you disable automatic updates, you will be required to update your runner version within 30 days of a new version being made available. You may want to subscribe to notifications for releases in the actions/runner repository. For more information, see Configuring notifications.

For instructions on how to install the latest runner version, see the installation instructions for the latest release.

Using webhooks for autoscaling

You can create your own autoscaling environment by using payloads received from the workflow_job webhook. This webhook is available at the repository, organization, and enterprise levels, and the payload for this event contains an action key that corresponds to the stages of a workflow job's life-cycle; for example when jobs are queued, in_progress, and completed. You must then create your own scaling automation in response to these webhook payloads.

• For more information about the workflow_job webhook, see Webhook events and payloads.
• To learn how to work with webhooks, see Webhooks documentation.

Authentication requirements

You can register and delete repository and organization self-hosted runners using the API. To authenticate to the API, your autoscaling implementation can use an access token or a GitHub app.

Your access token will require the following scope:

• For private repositories, use an access token with the repo scope.
• For public repositories, use an access token with the public_repo scope.
• For organizations, use an access token with the admin:org scope.

To authenticate using a GitHub App, it must be assigned the following permissions:

• For repositories, assign the administration permission.
• For organizations, assign the organization_self_hosted_runners permission.

You can register and delete enterprise self-hosted runners using the API. To authenticate to the API, your autoscaling implementation can use an access token.

Your access token will require the manage_runners:enterprise scope.