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In this guide, we’ll walk through signing and verifying an OCI artifact using Cosign and then configuring Flux CD to fetch and verify that artifact before deploying it in Kubernetes.

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Prerequisites

  • A fork or clone of the bb-appsource-git repository
  • Docker CLI installed and authenticated
  • A GitHub personal access token with read:packages and write:packages scopes
  • Flux CLI installed
  • A Cosign key pair generated (cosign.key and cosign.pub)

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1. Prepare the Repository

  1. Switch to a new feature branch: 
    git checkout -b 10-demo
  2. Under the manifests/ folder, confirm you have:
    • namespace.yaml
    • deployment.yaml
    • service.yaml
  3. Verify your deployment.yaml uses version 7.10.0: 
    apiVersion: apps/v1
kind: Deployment
metadata:
  name: block-buster
  labels:
    app: block-buster
    api: downward
    usage: global
spec:
  replicas: 1
  selector:
    matchLabels:
      app: block-buster
  template:
    metadata:
      labels:
        app: block-buster
        env: dev
        version: 7.10.0
    spec:
      containers:
      - name: app
        image: siddharth67/block-buster-dev:7.10.0
        imagePullPolicy: Always
        resources:
          requests:
            cpu: "100m"
            memory: "256Mi"

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2. Authenticate to GitHub Container Registry

Log in to GitHub Container Registry (GHCR) using your username and personal access token: 
docker login ghcr.io --username sidd-harth-2
# Enter your GHCR token when prompted
Ensure your token has at least read:packages and write:packages scopes to push and pull images.

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3. Push the OCI Artifact with Flux

Package your manifests folder and push it as an OCI artifact: 
flux push artifact \
  oci://ghcr.io/sidd-harth-2/bb-app:7.10.0-$(git rev-parse --short HEAD) \
  --path="./manifests" \
  --source="$(git config --get remote.origin.url)" \
  --revision="7.10.0/$(git rev-parse --short HEAD)"
Expected output: 
pushing artifact to ghcr.io/sidd-harth-2/bb-app:7.10.0-d6c285f
artifact successfully pushed to ghcr.io/sidd-harth-2/bb-app:7.10.0-d6c285f@sha256:eda014...
Verify the new package under Packages → bb-app on GitHub.

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4. Sign the Artifact with Cosign

  1. Pull the image by tag: 
    docker pull ghcr.io/sidd-harth-2/bb-app:7.10.0-d6c285f
  2. Sign by digest: 
    cosign sign \
  --key ../cosign/cosign.key \
  ghcr.io/sidd-harth-2/bb-app@sha256:eda014...
Approve uploading to the transparency log when prompted. A .sig blob is now attached to your OCI package.

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5. Verify the Signature Locally

Use your public key to confirm the artifact’s integrity: 
cosign verify \
  --key ../cosign/cosign.pub \
  ghcr.io/sidd-harth-2/bb-app@sha256:eda014...
You should see: 
Verification for ghcr.io/sidd-harth-2/bb-app@sha256:eda014...
  - The cosign claims were validated
  - Evidence of claims in the transparency log was verified offline
  - The signatures were verified against the specified public key

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6. Configure Flux to Pull and Verify

  1. Change to your Flux cluster repo: 
    cd ~/block-buster/flux-clusters/dev-cluster
  2. Create an OCIRepository source for GHCR: 
    flux create source oci 10-demo-source-oci-bb-app \
  --url oci://ghcr.io/sidd-harth-2/bb-app \
  --tag 7.10.0-d6c285f \
  --secret-ref ghcr-auth \
  --provider generic \
  --export > 10-demo-source-oci-bb-app.yaml
  3. Edit 10-demo-source-oci-bb-app.yaml to include Cosign verification: 
    apiVersion: source.toolkit.fluxcd.io/v1beta2
kind: OCIRepository
metadata:
  name: 10-demo-source-oci-bb-app
  namespace: flux-system
spec:
  interval: 1m0s
  provider: generic
  url: oci://ghcr.io/sidd-harth-2/bb-app
  ref:
    tag: 7.10.0-d6c285f
  secretRef:
    name: ghcr-auth
  verify:
    provider: cosign
    secretRef:
      name: cosign-pub
  4. Apply the source: 
    kubectl apply -f 10-demo-source-oci-bb-app.yaml
  5. Ensure secrets exist: 
    kubectl -n flux-system get secret ghcr-auth cosign-pub
  6. Create and apply a Kustomization to deploy the manifests: 
    flux create kustomization 10-demo-kustomize-oci-bb-app \
  --source=OCIRepository/10-demo-source-oci-bb-app \
  --target-namespace=10-demo \
  --path="./" \
  --prune=false \
  --interval=10s \
  --export > 10-demo-kustomize-oci-bb-app.yaml

kubectl apply -f 10-demo-kustomize-oci-bb-app.yaml

​
7. Confirm Verification and Deployment

  1. Reconcile and check the OCI source status: 
    flux reconcile source oci -n flux-system 10-demo-source-oci-bb-app
flux get sources oci -n flux-system
    You should see READY True.
  2. Inspect the SourceVerified condition: 
    kubectl -n flux-system get ocirepository 10-demo-source-oci-bb-app -o yaml
  3. Verify deployment in the 10-demo namespace: 
    kubectl -n 10-demo get all
  4. Access the application on its NodePort (e.g., localhost:30010). You should see version 7.10.0 of Block Buster:
The image shows a "Block Buster" game interface with colorful blocks, a paddle, and a ball, set against a starry background. Game details like pod name, IP, and version are displayed at the top.

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