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.

Use Karpenter in Kubernetes

To use the Karpenter hardened image in Kubernetes, update your deployment manifests to reference the hardened image. Karpenter is deployed as a controller in your cluster, typically through a Helm chart, or you can also apply manifests directly. Replace <tag> with the desired tag.

For example, in your karpenter-controller.yaml file:

apiVersion: v1
kind: ServiceAccount
metadata:
  name: karpenter
  namespace: karpenter
imagePullSecrets:
  - name: karpenter-regcred
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: karpenter
  namespace: karpenter
spec:
  selector:
    matchLabels:
      app.kubernetes.io/name: karpenter
  template:
    metadata:
      labels:
        app.kubernetes.io/name: karpenter
    spec:
      serviceAccountName: karpenter
      containers:
        - name: controller
          image: dhi.io/karpenter:<tag>

Make sure to create an imagePullSecret in the karpenter namespace and attach it to the Karpenter ServiceAccount so the controller Pod can pull the image from your private repository in Docker Hub.

For more details about using Karpenter, refer to the Karpenter documentation⁠.

Non-hardened images vs Docker Hardened Images

Key differences

Why no shell or package manager?

Docker Hardened Images prioritize security through minimalism:

• Reduced attack surface: Fewer binaries mean fewer potential vulnerabilities
• Immutable infrastructure: Runtime containers shouldn't be modified after deployment
• Compliance ready: Meets strict security requirements for regulated environments

The hardened images intended for runtime don't contain a shell nor any tools for debugging. Common debugging methods for applications built with Docker Hardened Images include:

• Docker Debug⁠ to attach to containers
• Docker's Image Mount feature to mount debugging tools
• Ecosystem-specific debugging approaches

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.

For example, you can use Docker Debug:

docker debug <image-name>

or mount debugging tools with the Image Mount feature:

docker run --rm -it --pid container:my-container \
  --mount=type=image,source=dhi.io/busybox,destination=/dbg,ro \
  dhi.io/<image-name>:<tag> /dbg/bin/sh

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 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.

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

Switching to the hardened Karpenter image does not require any special changes. You can use it as a drop-in replacement for the standard Karpenter controller image in your existing workflows and configurations.

Migration steps

1. Update your image reference. For example:
   • From: public.ecr.aws/karpenter/controller:<tag>
   • To: dhi.io/karpenter:<tag>
2. All your existing environment variables, volume mounts, and network settings remain the same.

General migration considerations

While the specific configuration requires no changes, be aware of these general differences in Docker Hardened Images:

Troubleshoot 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.

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.