connaisseur
SecurityA Kubernetes admission controller to integrate container image signature verification and trust pinning into a cluster.
A Kubernetes admission controller to integrate container image signature verification and trust pinning into a cluster.
Pull the latest version of this image from the Ghost registry. Pulling requires authentication — generate a token and run docker login first (see Authentication below).
The Ghost catalog is public to browse, but pulling images requires an account. Generate a pull token below (or from your Account → Tokens page) — you'll get a ready-to-paste docker login command, then docker pull works.
The username is generated automatically (it looks like robot$<project>+<auto-id>, not the name you typed) and is included in the docker login command above. The secret is shown only once when you create the token.
All Ghost images are signed with cosign. Verifying the signature before deployment ensures the image has not been tampered with.
Install cosign via brew install cosign or download from the Sigstore releases page.
Reference this image in your Dockerfile as a base layer:
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:
registry.ghost-prod.alphabravo.io/ghost-base/<repository>:<tag><your-namespace>/dhi-<repository>:<tag>For the examples, you must first use docker login registry.ghost-prod.alphabravo.io to authenticate to the registry to pull the images.
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: registry.ghost-prod.alphabravo.io/ghost-base/connaisseur
tag: <tag>
See the upstream deployment guide for the full set of values and configuration options: .
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/.
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/.
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/.
| 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 |
Ghost hardened images prioritize security through minimalism:
The hardened images intended for runtime don't contain a shell nor any tools for debugging. Common debugging methods for applications built with Ghost hardened images include:
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=registry.ghost-prod.alphabravo.io/ghost-base/busybox,destination=/dbg,ro \
registry.ghost-prod.alphabravo.io/ghost-base/connaisseur:<tag> /dbg/bin/sh
Ghost 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:
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:
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.
To migrate your application to a Ghost hardened image, you must update your Dockerfile. At minimum, you must update the base image in your existing Dockerfile to a Ghost 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 Ghost 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 | Ghost 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 | Ghost hardened images may have different entry points than images such as Docker Official Images. Inspect entry points for Ghost 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
Ghost 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.
The hardened images intended for runtime don't contain a shell nor any tools for debugging. The recommended method for debugging applications built with Ghost 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.
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.
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.
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.
Ghost hardened images may have different entry points than images such as Docker Official Images. Use docker inspect
to inspect entry points for Ghost hardened images and update your Dockerfile if necessary.