Prerequisites

Before you can use any Docker Hardened Image, you must mirror the image repository from the catalog to your organization. To mirror the repository, select either Mirror to repository or View in repository > Mirror to repository, and then follow the on-screen instructions.

Start a startup-script instance

The cilium-startup-script image is designed to run as a DaemonSet in Kubernetes. It executes startup scripts on host nodes using the privileged nsenter command. The script content is provided via the STARTUP_SCRIPT environment variable.

Run the following command and replace with your organization's namespace and with the image variant you want to run.

docker run --rm --privileged --pid=host \
  -e STARTUP_SCRIPT='#!/bin/bash
echo "Hello from host namespace"' \
  <your-namespace>/dhi-cilium-startup-script:<tag>

Common startup-script use cases

Kubernetes DaemonSet deployment

Deploy as a DaemonSet to execute startup scripts on all nodes in a Kubernetes cluster.

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: startup-script
  labels:
    app: startup-script
spec:
  selector:
    matchLabels:
      app: startup-script
  template:
    metadata:
      labels:
        app: startup-script
    spec:
      hostPID: true
      containers:
        - name: startup-script
          image: <your-namespace>/dhi-cilium-startup-script:<tag>
          securityContext:
            privileged: true
          env:
            - name: STARTUP_SCRIPT
              value: |
                #!/bin/bash
                set -o errexit
                set -o pipefail
                set -o nounset

                # Your startup commands here
                echo "Initializing node..."

Node configuration and setup

Execute one-time configuration on Kubernetes nodes, with automatic checkpoint-based idempotency.

env:
  - name: STARTUP_SCRIPT
    value: |
      #!/bin/bash
      # Configure system settings
      sysctl -w net.ipv4.ip_forward=1

      # Install or configure node-level components
      echo "Node setup complete"
  - name: CHECKPOINT_PATH
    value: /tmp/node-configured

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-image \
  --mount=type=image,source=<your-namespace>/dhi-busybox,destination=/dbg,ro \
  <your-namespace>/<image-name>:<tag> /dbg/bin/sh

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

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.

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.

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.