How to use this image

All examples in this guide use the public image. If you've mirrored the repository for your own use (for example, to your Docker Hub namespace), update your commands to reference the mirrored image instead of the public one.

For example:

• Public image: dhi.io/actions-runner:<tag>
• Mirrored image: <your-namespace>/dhi-actions-runner:<tag>

For the examples, you must first use docker login dhi.io to authenticate to the registry to pull the images.

What's included in this actions-runner image

This Docker Hardened actions-runner image includes:

• The GitHub Actions runner (config.sh, run.sh, and the underlying Runner.Listener binary), installed under /usr/lib/actions-runner
• git, curl, jq, and unzip, used by the runner and by actions/steps that shell out to them
• The Docker CLI and docker buildx plugin, for workflows that run Docker container actions or docker build steps directly against a mounted or sidecar Docker daemon. This image has no docker group, so a mounted or sidecar Docker socket is only usable by nonroot if you add its GID with docker run --group-add <socket-gid> (or the equivalent field on your scheduler), matching whatever group actually owns the socket you're mounting.
• Container hooks⁠ for both Kubernetes (k8s) and Docker (docker) execution modes, staged under /usr/share/gha-runner-container-hooks/{k8s,docker}, for use with the Actions Runner Controller⁠

Start an actions-runner container

Check the version

$ docker run --rm dhi.io/actions-runner:<tag> --version

Register and run a runner

The runner is a two-step process: config.sh registers the runner with a repository or organization, then run.sh starts listening for jobs. Both scripts live under /usr/lib/actions-runner, which is owned by the nonroot user so the runner can write its own registration state (.runner, .credentials) and work/diag directories directly alongside its binaries.

Because registration state lives inside that same directory, don't mount a volume over the whole /usr/lib/actions-runner path - doing so shadows the runner binaries themselves, and since Docker only seeds a named volume from the image on its first use, later docker pulls of a newer image tag would never reach the runner tree underneath it. Run registration and the listener as a single container instead, so both steps see the same image-provided binaries:

$ docker run -d --name actions-runner \
  --entrypoint /bin/bash \
  dhi.io/actions-runner:<tag> \
  -c '[ -f /usr/lib/actions-runner/.runner ] || /usr/lib/actions-runner/config.sh --url https://github.com/<org>/<repo> --token <registration-token> --unattended; exec /usr/lib/actions-runner/run.sh'

The [ -f .runner ] || guard is required: config.sh refuses to run again once a .runner file exists, so without it a docker start on this same container - which re-runs the full docker run command, not just run.sh - would fail before run.sh ever started. With the guard, docker start/docker stop work as expected across restarts, since the registration state lives in that container's writable layer. To pick up a newer image, register a fresh container from the new tag (and deregister the old one) rather than trying to carry state over.

Kubernetes with Actions Runner Controller (recommended)

For Kubernetes deployments, use the Actions Runner Controller⁠ with container hooks, so each job step that specifies a container runs in its own ephemeral Pod instead of requiring a Docker socket in the runner container. ARC's chart defaults assume the upstream image's /home/runner layout, so you must override both the listener command and, for the dind template, the path its init container copies externals from - otherwise the runner container crash-loops on a path that doesn't exist in this image:

template:
  spec:
    containers:
      - name: runner
        command: ["/usr/lib/actions-runner/run.sh"]
        env:
          - name: ACTIONS_RUNNER_CONTAINER_HOOKS
            value: /usr/share/gha-runner-container-hooks/k8s/index.js

If you use the gha-runner-scale-set dind template, also update its init container to copy from /usr/lib/actions-runner/externals instead of the chart's default /home/runner/externals.

Environment variables

Non-hardened images vs. Docker Hardened Images

The upstream ghcr.io/actions/actions-runner image installs the runner directly into /home/runner and creates a runner user with passwordless sudo and Docker group membership. This Docker Hardened Image installs the runner under /usr/lib/actions-runner and runs as the standard DHI nonroot user (uid 65532) instead - the runner's registration state and work directories still need to live alongside its binaries (this is an upstream constraint, not a DHI convention), so that specific directory is owned by nonroot rather than being read-only. sudo is not included: the image has no root entry in its user database, so a setuid-root sudo binary would not function anyway. Workflow steps that need root-only operations should use a dev variant or a dedicated privileged step instead.

Image variants

Docker Hardened Images come in different variants depending on their intended use. Image variants are identified by their tag.

• Runtime variants are designed to run your application in production. These images are intended to be used either directly or as the FROM image in the final stage of a multi-stage build. These images typically:

  • Run as a nonroot user
  • Do not include a shell or a package manager
  • Contain only the minimal set of libraries needed to run the app

• Build-time variants typically include dev in the tag name and are intended for use in the first stage of a multi-stage Dockerfile. These images typically:

  • Run as the root user
  • Include a shell and package manager
  • Are used to build or compile applications

• FIPS variants include fips in the variant name and tag. They come in both runtime and build-time variants. These variants use cryptographic modules that have been validated under FIPS 140, a U.S. government standard for secure cryptographic operations. For example, usage of MD5 fails in FIPS variants.

To view the image variants and get more information about them, select the Tags tab for this repository, and then select a tag.

Migrate to a Docker Hardened Image

To migrate your application to a Docker Hardened Image, you must update your Dockerfile. At minimum, you must update the base image in your existing Dockerfile to a Docker Hardened Image. This and a few other common changes are listed in the following table of migration notes.

The following steps outline the general migration process.

1. Find hardened images for your app.

   A hardened image may have several variants. Inspect the image tags and find the image variant that meets your needs.

2. Update the base image in your Dockerfile.

   Update the base image in your application's Dockerfile to the hardened image you found in the previous step. For framework images, this is typically going to be an image tagged as dev because it has the tools needed to install packages and dependencies.

3. For multi-stage Dockerfiles, update the runtime image in your Dockerfile.

   To ensure that your final image is as minimal as possible, you should use a multi-stage build. All stages in your Dockerfile should use a hardened image. While intermediary stages will typically use images tagged as dev, your final runtime stage should use a non-dev image variant.

4. Install additional packages

   Docker Hardened Images contain minimal packages in order to reduce the potential attack surface. You may need to install additional packages in your Dockerfile. Inspect the image variants to identify which packages are already installed.

   Only images tagged as dev typically have package managers. You should use a multi-stage Dockerfile to install the packages. Install the packages in the build stage that uses a dev image. Then, if needed, copy any necessary artifacts to the runtime stage that uses a non-dev image.

   For Debian-based images, you can use apt-get to install packages.

Troubleshooting migration

The following are common issues that you may encounter during migration.

General debugging

The hardened images intended for runtime don't contain a shell nor any tools for debugging. The recommended method for debugging applications built with Docker Hardened Images is to use Docker Debug⁠ to attach to these containers. Docker Debug provides a shell, common debugging tools, and lets you install other tools in an ephemeral, writable layer that only exists during the debugging session.

Permissions

By default image variants intended for runtime, run as the nonroot user. Ensure that necessary files and directories are accessible to the nonroot user. You may need to copy files to different directories or change permissions so your application running as the nonroot user can access them.

Privileged ports

Non-dev hardened images run as a nonroot user by default. As a result, applications in these images can't bind to privileged ports (below 1024) when running in Kubernetes or in Docker Engine versions older than 20.10. To avoid issues, configure your application to listen on port 1025 or higher inside the container, even if you map it to a lower port on the host. For example, docker run -p 80:8080 my-image will work because the port inside the container is 8080, and docker run -p 80:81 my-image won't work because the port inside the container is 81.

No shell

By default, image variants intended for runtime don't contain a shell. Use dev images in build stages to run shell commands and then copy any necessary artifacts into the runtime stage. In addition, use Docker Debug to debug containers with no shell.

Entry point

Docker Hardened Images may have different entry points than images such as Docker Official Images. Use docker inspect to inspect entry points for Docker Hardened Images and update your Dockerfile if necessary.