How to use this image

The image ships the tkn binary as its entrypoint, so arguments are passed straight through.

# Print the client version
docker run --rm dhi.io/tkn:<version> version

# Show available commands
docker run --rm dhi.io/tkn:<version> --help

Connecting to a cluster

tkn resolves cluster credentials the same way kubectl does. Mount a kubeconfig and point KUBECONFIG at it:

docker run --rm \
  -v "$HOME/.kube/config:/kubeconfig:ro" \
  -e KUBECONFIG=/kubeconfig \
  dhi.io/tkn:<version> pipeline list

When running as a step image inside a Tekton Task, the injected ServiceAccount token is used automatically and no kubeconfig is required.

Following pipeline logs

docker run --rm \
  -v "$HOME/.kube/config:/kubeconfig:ro" \
  -e KUBECONFIG=/kubeconfig \
  dhi.io/tkn:<version> pipelinerun logs -f <pipelinerun-name>

Working with OCI bundles

tkn bundle packages Tekton resources into an OCI image and reads them back. It talks to a registry and needs no cluster:

# Package a Task into a bundle
docker run --rm -v "$PWD:/work:ro" -w /work \
  dhi.io/tkn:<version> bundle push registry.example.com/tekton/my-task:v1 -f task.yaml

# List the resources inside a bundle
docker run --rm dhi.io/tkn:<version> bundle list registry.example.com/tekton/my-task:v1

Registry credentials are read from a Docker or Podman config file. Mount one and set DOCKER_CONFIG to its directory.

Using it in a Tekton Task

The runtime variant has no shell, so a step invokes tkn through args rather than through a script block:

apiVersion: tekton.dev/v1
kind: Task
metadata:
  name: list-pipelines
spec:
  steps:
    - name: tkn
      image: dhi.io/tkn:<version>
      args: ["pipeline", "list"]

Tasks written against the upstream tkn image often use a script block instead, which Tekton executes with /bin/sh. Those steps fail on the runtime variant:

exec: "/bin/sh": stat /bin/sh: no such file or directory

There are two ways to migrate such a step:

• If it only invokes tkn, replace the script block with args, as above.
• If it needs shell logic such as conditionals, command substitution or eval, use dhi.io/tkn:<version>-dev, which includes a shell. It runs as root by default, and a securityContext that pins runAsUser still applies.

Color and emoji output

tkn disables color and emojis automatically when output is piped or run non-interactively, such as from a Tekton Task. To disable them explicitly, set NO_COLOR or pass --no-color:

docker run --rm -e NO_COLOR="" dhi.io/tkn:<version> taskrun describe <name>

Best practices

• Pin to a full version tag in production rather than a floating major tag
• Mount kubeconfig read-only and prefer a ServiceAccount when running in-cluster
• Use the runtime variant for Task steps that invoke tkn directly, and -dev for steps that need a shell

Common issues

• Couldn't get kubeConfiguration namespace — no kubeconfig was found. Mount one and set KUBECONFIG, or run with a ServiceAccount in-cluster.
• bundle push fails to authenticate — mount a registry config and set DOCKER_CONFIG to the directory containing config.json.
• stat /bin/sh: no such file or directory — the runtime variant has no shell. Convert the step to args, or use the -dev variant.

Image variants

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

Available image tags for tkn:

Tag selection guidance:

• Use dhi.io/tkn:<version> for standard production deployments
• Use dhi.io/tkn:<version>-fips for FIPS-compliant environments
• Use major version tags (like :<major>) for automatic minor updates (not recommended for production)
• Use -dev variants only in the first stage of a multi-stage build or for interactive debugging

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.