Building an OCI-native Container Image CI/CD Pipeline¶

An OCI-native secure container image build/delivery pipeline using the following tools:

• stacker for building OCI images

• zot as a vendor-neutral OCI image registry server

• skopeo for performing repository interactions

• cosign for container signing and verification

• cri-o for deploying container images

• cosigned for validating container images before deployment

The Open Container Initiative (OCI) is an open governance structure for the express purpose of creating open industry standards around container formats and runtimes.

This document describes a step-by-step procedure towards achieving an OCI-native secure software supply chain using zot in collaboration with other open source tools. The following diagram shows a portion of the CI/CD pipeline.

Build images¶

stacker is a standalone tool for building OCI images via a declarative yaml format. The output of the build process is a container image in an OCI layout.

example: stacker build command

stacker build -f <stackerfile.yaml>

Image registry¶

zot is a production-ready vendor-neutral OCI image registry server purely based on the OCI Distribution Specification. If stacker is used to build the OCI image, it can also be used to publish the built image to an OCI registry.

example: stacker publish command

stacker publish --url <url> --username <user> --password <password>

Alternatively, you can use skopeo, a command line utility that performs various operations on container images and image repositories.

example: skopeo copies an image to a registry

skopeo copy --format=oci oci:<oci-dir>/image:tag \
  docker://<zot-server>/image:tag

Signing images¶

cosign is a tool that performs container signing, verification, and storage in an OCI registry.

example: cosign generates keys and signs an image in the registry

cosign generate-key-pair

cosign sign --key cosign.key <zot-server>/image:tag

Deploying container images¶

cri-o is an implementation of the Kubernetes Container Runtime Interface (CRI) to enable using OCI compatible runtimes. It is a lightweight alternative to using Docker as the runtime for Kubernetes.

zot is compatible with kubernetes/cri-o using docker:// transport, which is the default.

example: kubelet configuration file

apiVersion: v1
kind: Pod
metadata:
  name: example-pod
spec:
  containers:
  - name: example-container
    image: <zot-server>/image:tag

Container image verification¶

cosigned is an image admission controller that validates container images before deploying them.

example: install cosigned using Helm

kubectl create namespace cosign-system

kubectl create secret generic mysecret -n \
  cosign-system --from-file=cosign.pub=./cosign.pub

helm repo add sigstore https://sigstore.github.io/helm-charts

helm repo update

helm install cosigned -n cosign-system sigstore/cosigned \
  --devel --set cosign.secretKeyRef.name=mysecret