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/portieris:<tag>
• Mirrored image: <your-namespace>/dhi-portieris:<tag>

For the examples, you must first use docker login dhi.io to authenticate to the registry to pull the images.

What's included

This image packages the portieris binary, a Kubernetes mutating admission webhook that enforces image security policies defined in ImagePolicy and ClusterImagePolicy resources. It serves the webhook over HTTPS on port 8000 (/admit, /health/liveness, /health/readiness) and Prometheus metrics over HTTP on port 8080 (/metrics). See the upstream project⁠ and its policy reference⁠ for the full policy syntax.

Install Portieris with the upstream Helm chart

Portieris runs inside a Kubernetes cluster. The upstream Helm chart, published with each release⁠, installs the CRDs, the Deployment, the Service, the RBAC and the MutatingWebhookConfiguration. Point its image.host, image.image and image.tag values at this image, and set securityContext.runAsUser to 65532: the chart defaults to 1000060001, which can't write the image's /run work directory.

Download and unpack the chart for the release that matches the image tag, then generate the webhook certificates for the portieris namespace with the script the chart ships (it needs bash and openssl):

$ curl -fsSLO https://github.com/IBM/portieris/releases/download/v<version>/portieris-v<version>.tgz
$ tar xzf portieris-v<version>.tgz
$ bash portieris/gencerts portieris

Create the namespace and a pull secret for dhi.io, then install the chart:

$ kubectl create namespace portieris
$ kubectl create secret docker-registry dhi-pull --namespace portieris \
  --docker-server=dhi.io --docker-username=<username> --docker-password=<access-token>
$ helm install portieris ./portieris --namespace portieris \
  --set image.host=dhi.io \
  --set image.image=portieris \
  --set image.tag=<tag> \
  --set image.pullSecret=dhi-pull \
  --set securityContext.runAsUser=65532
$ kubectl --namespace portieris rollout status deployment/portieris

The chart's ImagePolicy in the portieris namespace allows dhi.io/portieris, so Portieris can admit its own pods.

Common Portieris use cases

Allow images cluster-wide

With the chart's default PolicySet: None, Portieris denies every image in a namespace that has no ImagePolicy while no ClusterImagePolicy exists. Create a ClusterImagePolicy that lists the repositories your cluster may run:

$ kubectl apply -f - <<'EOF'
apiVersion: portieris.cloud.ibm.com/v1
kind: ClusterImagePolicy
metadata:
  name: allow-trusted-registries
spec:
  repositories:
    - name: "registry.example.com/*"
EOF

Restrict one namespace

An ImagePolicy in a namespace replaces the cluster policies for that namespace. A pattern can carry a wildcard inside the path:

$ kubectl create namespace payments
$ kubectl apply -f - <<'EOF'
apiVersion: portieris.cloud.ibm.com/v1
kind: ImagePolicy
metadata:
  name: payments-only
  namespace: payments
spec:
  repositories:
    - name: "registry.example.com/payments/*"
    - name: "registry.example.com/*/sidecar"
EOF

A pod in payments whose image no pattern matches is refused by the webhook:

$ kubectl run web --namespace payments --image=registry.example.com/web/app:1 --dry-run=server
Error from server: admission webhook "trust.hooks.securityenforcement.admission.cloud.ibm.com" denied the request:
Deny "registry.example.com/web/app:1", no matching repositories in the ImagePolicies

Require signed images

A simple policy admits an image only when it carries a signature from the key in its keySecret Secret, which holds the armored public key under key. storeURL names the lookaside store that serves the signatures when the registry does not serve them itself:

$ kubectl create namespace releases
$ gpg --export --armor <fingerprint> > signer.pub
$ kubectl create secret generic signer-key --namespace releases --from-file=key=signer.pub
$ kubectl apply -f - <<'EOF'
apiVersion: portieris.cloud.ibm.com/v1
kind: ImagePolicy
metadata:
  name: releases-signed
  namespace: releases
spec:
  repositories:
    - name: "registry.example.com/releases/*"
      policy:
        simple:
          requirements:
            - type: signedBy
              keySecret: signer-key
          storeURL: https://sigstore.example.com
EOF

The webhook rewrites an admitted image to the digest the signature covers. It refuses an unsigned image with simple: policy denied the request: A signature was required, but no signature exists, and an image signed by another key with Key not found for key ID <id> in signature.

Monitor admission decisions

The webhook counts its decisions in portieris_pod_admission_decision_allow_count and portieris_pod_admission_decision_deny_count on port 8080. The chart annotates the pods with prometheus.io/scrape and prometheus.io/port: "8080" for annotation-based scraping. To read the counters directly:

$ kubectl --namespace portieris port-forward deployment/portieris 8080:8080
$ curl -s http://127.0.0.1:8080/metrics | grep portieris_pod_admission_decision

Non-hardened images vs. Docker Hardened Images

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 a 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 tag 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

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.

Troubleshooting 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.

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. To avoid issues, configure your application to listen on port 1025 or higher inside the container, even if you map it to a lower port on the host. For example, docker run -p 80:8080 my-image will work because the port inside the container is 8080, and docker run -p 80:81 my-image won't work because the port inside the container is 81.

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.