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/<repository>:<tag>
• Mirrored image: <your-namespace>/dhi-<repository>:<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 forklift-controller image

This Docker Hardened Forklift Controller image is a component of the Forklift⁠ VM migration operator for KubeVirt.

• forklift-controller: reconciles Forklift providers, plans, mappings, hooks, and migrations, and drives each virtual machine migration from inventory discovery through disk transfer

Forklift migrates virtual machines from VMware vSphere, oVirt, OpenStack, Hyper-V, EC2, and OVA sources to KubeVirt. The controller is one of several Forklift components and is normally deployed by the Forklift operator as part of a full Forklift installation.

Key differences

The upstream image installs tar so that files can be copied out of a running pod, for example with kubectl cp or during a must-gather. It is omitted from the hardened runtime variants to keep the attack surface minimal. If you need to retrieve files from a running container, use Docker Debug⁠, or use the dev variant, which includes a shell and a package manager.

Run the forklift-controller container

The controller is designed to run inside a Kubernetes cluster with access to the Kubernetes API and to the Forklift custom resources. Running it standalone is useful mainly to verify the image starts.

The ROLE environment variable selects which roles the controller runs. It accepts main, inventory, or a comma-separated combination. When ROLE is unset, both roles are enabled.

The main role requires the migration settings that the Forklift operator normally injects, so the shortest way to check the image is to start the inventory role only:

docker run --rm -e ROLE=inventory dhi.io/forklift-controller:<tag>

Without a reachable cluster the controller logs its metrics and profiling endpoints, then exits when it cannot load a kube config. That is the expected standalone behavior.

Ports

This image changes none of the controller's defaults, so it listens exactly where the upstream image does. Only 2112 is declared on the image, because it is the only port the controller binds unconditionally; the other two depend on ROLE and on the port variables below.

API_PORT and METRICS_PORT both default to 8080, so on the bare defaults the inventory API and the controller manager metrics server compete for the same socket. Whichever binds second fails with listen tcp :8080: bind: address already in use and the controller exits. This is upstream behavior, not something this image introduces.

A normal Forklift install never hits it because the operator sets both ports explicitly: its main container gets API_PORT=8443 and METRICS_PORT=8081, and its inventory container gets API_PORT=8443 and METRICS_PORT=8082. Use the same values if you deploy the container yourself:

env:
  - name: ROLE
    value: inventory
  - name: API_PORT
    value: "8443"
  - name: METRICS_PORT
    value: "8082"

The inventory API serves plain HTTP unless you also set API_TLS_CERTIFICATE and API_TLS_KEY, which is what the operator mounts from its TLS secret.

Port 2112 is served by Go's default HTTP mux, and the controller imports net/http/pprof, so that listener exposes the /debug/pprof handlers alongside /metrics. This is upstream behavior and is not configurable through the image. Treat 2112 as a privileged debug port: keep it inside the cluster, and do not publish it to untrusted networks. The same handlers are also reachable on port 6060, which the controller binds to localhost inside the container only.

Deploy Forklift in Kubernetes

The recommended way to deploy Forklift, including the controller, is with the Forklift operator. See the Forklift documentation⁠ for installation instructions and for the provider, mapping, plan, and migration resources the controller reconciles.

Image variants

Docker Hardened Images come in different variants depending on their intended use.

• 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 the 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 variant 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.

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 Alpine-based images, you can use apk to install packages. 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.