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 kyverno-cli Hardened image

This image contains kyverno-cli, the official Kyverno CLI tool for managing Kubernetes Native Policy Management. The entry point for the image is kyverno-cli which provides policy creation and validation, resource testing against policies, policy application and management, and integration with CI/CD pipelines for GitOps workflows.

Start a kyverno-cli instance

Run the following command and replace <tag> with the image variant you want to run.

Note:kyverno-cli is designed as a CLI tool for policy management and can be used in CI/CD pipelines, local development, or as part of GitOps workflows.

docker run --rm -it dhi.io/kyverno-cli:<tag> --help

Common kyverno-cli use cases

Validate policies and resources

kyverno-cli can validate Kyverno policies and test resources against those policies without requiring a Kubernetes cluster. This is especially useful in CI/CD pipelines for policy validation.

# Validate a policy file
docker run --rm -v $(pwd):/workspace dhi.io/kyverno-cli:<tag> \
  validate /workspace/my-policy.yaml

# Test a resource against policies (apply command)
docker run --rm -v $(pwd):/workspace dhi.io/kyverno-cli:<tag> \
  apply /workspace/my-policy.yaml --resource /workspace/my-resource.yaml

Available kyverno-cli commands

The kyverno-cli CLI provides several key commands:

# Main Commands:
# apply     - Apply policies on resources (dry-run validation)
# test      - Run tests from directory (comprehensive test suites)  
# validate  - Validate policies and resources
# create    - Create Kyverno resources
# jp        - JMESPath query testing
# version   - Show version information

# Run policy tests from a test directory
docker run --rm -v $(pwd):/workspace dhi.io/kyverno-cli:<tag> \
  test /workspace/kyverno-tests/

# Test JMESPath expressions (useful for policy development)
docker run --rm -v $(pwd):/workspace dhi.io/kyverno-cli:<tag> \
  jp query 'spec.containers[*].image' --input /workspace/resource.yaml

# Create Kyverno resources
docker run --rm -v $(pwd):/workspace dhi.io/kyverno-cli:<tag> \
  create <resource-type>

Use kyverno-cli in CI/CD pipelines

kyverno-cli is commonly used in CI/CD pipelines for policy validation and resource testing. Here's an example GitHub Actions workflow:

name: Policy Validation
on: [push, pull_request]

jobs:
  validate-policies:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3

      - name: Validate Kyverno Policies
        run: |
          docker run --rm -v ${{ github.workspace }}:/workspace \
            dhi.io/kyverno-cli:<tag> \
            validate /workspace/policies/

      - name: Test Resources Against Policies
        run: |
          docker run --rm -v ${{ github.workspace }}:/workspace \
            dhi.io/kyverno-cli:<tag> \
            apply /workspace/policies/ --resource /workspace/manifests/

      - name: Run Policy Test Suite
        run: |
          docker run --rm -v ${{ github.workspace }}:/workspace \
            dhi.io/kyverno-cli:<tag> \
            test /workspace/kyverno-tests/

Local policy development and testing

Use kyverno-cli for local development and testing of Kyverno policies:

# Create an alias for easier usage
alias kyverno='docker run --rm -v $(pwd):/workspace dhi.io/kyverno-cli:<tag>'

# Validate policies
kyverno validate my-policy.yaml

# Test JMESPath expressions
kyverno jp query 'spec.containers[0].image' --input my-resource.yaml

# Apply policies to resources
kyverno apply my-policy.yaml --resource my-resource.yaml

# Check version
kyverno version

GitOps integration

Integrate kyverno-cli into your GitOps workflows for automated policy validation:

# Pre-commit hook example
#!/bin/bash
# .git/hooks/pre-commit

echo "Validating Kyverno policies..."
docker run --rm -v $(pwd):/workspace \
  dhi.io/kyverno-cli:<tag> \
  validate /workspace/k8s/policies/

if [ $? -ne 0 ]; then
  echo "Policy validation failed. Commit rejected."
  exit 1
fi

echo "Policy validation passed."

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

Hardened image debugging

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 dhi.io/kyverno-cli

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/kyverno-cli:<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

Migrate to a Docker Hardened Image

To migrate your application to a Docker Hardened Image, you must update your Kubernetes manifests or Docker configurations. At minimum, you must update the base image in your existing deployment 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 CLI usage.

   A hardened image may have several variants. Inspect the image tags and find the image variant that meets your needs. The kyverno-cli CLI is typically used in CI/CD pipelines and local development environments.

2. Update your CI/CD pipeline configurations.

   Update the image references in your CI/CD scripts, GitHub Actions, or other automation to use the hardened images:

   • From: kyverno/kyverno-cli:<tag>
   • To: dhi.io/kyverno-cli:<tag>

3. For custom containers, update the base image in your Dockerfile.

   If you're building custom images that include kyverno-cli, ensure that your final image uses the hardened kyverno-cli as the base. For multi-stage builds, use images tagged as dev for build stages and non-dev images for runtime.

4. Update volume mounting and file access patterns.

   Ensure your scripts properly mount volumes and access policy files and resources. The kyverno-cli CLI needs access to policy files and resource manifests through proper volume mounting.

5. Test CLI functionality.

   After migration, verify that policy validation, resource testing, and other CLI operations continue to function correctly with the hardened image. Test common workflows like apply, validate, and test commands.

Troubleshoot 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.

kyverno-cli requires read access to policy files and resource manifests. Ensure your volume mounts and file permissions allow the nonroot user to access these files when running in containers.

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.