dhi.io/connaisseur
Connaisseur
A Kubernetes admission controller to integrate container image signature verification and trust pinning into a cluster.
Prerequisites
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.
Start a Connaisseur instance
Connaisseur is a Kubernetes admission controller that intercepts pod creation and update requests to verify container image signatures against configured trust policies. It requires a configuration file, TLS certificates, and is intended to be deployed as a webhook in a Kubernetes cluster.
Because Connaisseur is designed as a Kubernetes admission webhook, the recommended way to run it is via the upstream Helm chart. To deploy Connaisseur with the hardened image, override the image repository and tag in your Helm values:
# values.yaml
kubernetes:
deployment:
image:
repository: dhi.io/connaisseur
tag: <tag>
See the upstream deployment guide for the full set of values and configuration options: https://sse-secure-systems.github.io/connaisseur/latest/basics/#deploy.
Common Connaisseur use cases
Enforce cosign image signature verification
Configure Connaisseur to validate container image signatures using cosign by defining a cosign validator and
associating it with one or more image patterns in your trust policy. Supply the public key(s) under
validators[].trustRoots and reference them from policy[].with.trustRoot.
See the upstream validator reference for the full schema: https://sse-secure-systems.github.io/connaisseur/latest/validators/sigstore_cosign/.
Deny unsigned images
Use a static validator with approve: false to block specific image patterns that must never be admitted. Combine it
with a default-approve validator and scope the deny rule to the registries or paths you want to restrict.
See the upstream validators reference for the exact fields, supported types, and evaluation order: https://sse-secure-systems.github.io/connaisseur/latest/validators/.
Configure alerting for admission decisions
Connaisseur can send alerts on admit and reject decisions through Slack, OpsGenie, and other receivers. Configure
alerting.admitRequest and alerting.rejectRequest with one or more receiver templates and their webhook URLs.
See the upstream alerting guide for supported templates, payload variables, and failure behavior: https://sse-secure-systems.github.io/connaisseur/latest/features/alerting/.
Non-hardened images vs Docker Hardened Images
Key differences
| Feature | Non-hardened Connaisseur | Docker Hardened Connaisseur |
|---|---|---|
| Security | Standard base with common utilities | Minimal, hardened base with security patches |
| Shell access | Full shell (bash/sh) available | No shell in runtime variants |
| Package manager | apt/apk available | No package manager in runtime variants |
| User | Runs as root by default | Runs as nonroot user |
| Attack surface | Larger due to additional utilities | Minimal, only essential components |
| Debugging | Traditional shell debugging | Use Docker Debug or Image Mount for troubleshooting |
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 <container-name>
or mount debugging tools with the Image Mount feature:
docker run --rm -it --pid container:my-connaisseur \
--mount=type=image,source=dhi.io/busybox,destination=/dbg,ro \
dhi.io/connaisseur:<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.
FIPS variants of Connaisseur set GODEBUG=fips140=on and use a FIPS-validated Go cryptographic module. To verify FIPS
compliance, check that the cryptographic module version is in use by your Connaisseur instance.
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:
| Item | Migration note |
|---|---|
| Base image | Replace your base images in your Dockerfile with a Docker Hardened Image. |
| Package management | Non-dev images, intended for runtime, don't contain package managers. Use package managers only in images with a dev tag. |
| Non-root user | By default, non-dev images, intended for runtime, run as the nonroot user. Ensure that necessary files and directories are accessible to the nonroot user. |
| Multi-stage build | Utilize images with a dev tag for build stages and non-dev images for runtime. For binary executables, use a static image for runtime. |
| TLS certificates | Docker Hardened Images contain standard TLS certificates by default. There is no need to install TLS certificates. |
| 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. Connaisseur default port 5000 works without issues. |
| Entry point | Docker Hardened Images may have different entry points than images such as Docker Official Images. Inspect entry points for Docker Hardened Images and update your Dockerfile if necessary. |
| No shell | By default, non-dev images, intended for runtime, don't contain a shell. Use dev images in build stages to run shell commands and then copy artifacts to the runtime stage. |
The following steps outline the general migration process.
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.
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.
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.
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.