Get started using the Google Cloud CLI (GKE)

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The terms: whitelist

Note: This tutorial assumes that you have read the Binary Authorization overview.

This tutorial shows how to configure and test a Binary Authorization policy that requires attestations. This type of policy secures your container-based software supply chain by verifying that a container image has a signed attestation before allowing deployment of the image.

At deploy time, Binary Authorization uses attestors to verify digital signatures in attestations. The attestations are created by signers, usually as part of a continuous integration (CI) pipeline.

In this tutorial, the GKE cluster, attestations, and attestors are all located in a single project. A single-project configuration is mostly useful for testing or experimenting with the service. For a more real-world example, see multi-project configuration.

The steps below describe tasks that you perform at the command line. To follow these steps using Google Cloud console, see Get started using the console.

Objectives

In this tutorial, you learn how to:

• Create a Google Kubernetes Engine (GKE) cluster with Binary Authorization enabled
• Create an attestor that the Binary Authorization enforcer uses to verify the signature on an attestation
• Configure a policy that requires an attestation
• Create a cryptographic key pair to sign attestations and later verify them
• Sign a container image digest, creating a signature
• Create an attestation using the signature
• Test the policy by deploying a container image to GKE

Costs

This tutorial uses the following billable components of Google Cloud:

• Artifact Registry or Container Registry
• Binary Authorization
• GKE
• Optional: Cloud Key Management Service

To generate a cost estimate based on your projected usage, use the pricing calculator. New Google Cloud users might be eligible for a free trial.

Before you begin

1. Sign in to your Google Cloud account. If you're new to Google Cloud, create an account to evaluate how our products perform in real-world scenarios. New customers also get $300 in free credits to run, test, and deploy workloads.

2. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

3. Make sure that billing is enabled for your Cloud project. Learn how to check if billing is enabled on a project.

4. Install and initialize the Google Cloud CLI.

5. In the Google Cloud console, on the project selector page, select or create a Google Cloud project.

   Note: If you don't plan to keep the resources that you create in this procedure, create a project instead of selecting an existing project. After you finish these steps, you can delete the project, removing all resources associated with the project.

   Go to project selector

6. Make sure that billing is enabled for your Cloud project. Learn how to check if billing is enabled on a project.

7. Install and initialize the Google Cloud CLI.
8. Install kubectl for interacting with GKE.

Enable Binary Authorization

Set the default project

The first step is to set the default Google Cloud project used by the gcloud command:

PROJECT_ID=PROJECT_ID
gcloud config set project ${PROJECT_ID}

where PROJECT_ID is the name of your project.

Enable required APIs

Enable APIs for:

Container Registry

gcloud --project=${PROJECT_ID} \
    services enable\
    container.googleapis.com\
    containerregistry.googleapis.com\
    binaryauthorization.googleapis.com

Artifact Registry

gcloud --project=${PROJECT_ID} \
    services enable\
    container.googleapis.com\
    artifactregistry.googleapis.com\
    binaryauthorization.googleapis.com

Create a cluster with Binary Authorization enabled

Create the cluster

Create a GKE cluster with Binary Authorization enabled. This is the cluster where you want your deployed container images to run. When you create the cluster, you pass the --binauthz-evaluation-mode=PROJECT_SINGLETON_POLICY_ENFORCE flag to the gcloud container clusters create command.

To create the cluster, follow these steps:

gcloud container clusters create \
    --binauthz-evaluation-mode=PROJECT_SINGLETON_POLICY_ENFORCE \
    --zone us-central1-a \
    test-cluster

Here, you create a cluster named test-cluster in the GKE zone us-central1-a.

Configure kubectl

You must also update the local kubeconfig file for your kubectl installation. This provides the credentials and endpoint information required to access the cluster in GKE.

To update the local kubeconfig file:

gcloud container clusters get-credentials \
    --zone us-central1-a \
    test-cluster

View the default policy

A policy in Binary Authorization is a set of rules that govern the deployment of container images. You can have one policy per project. By default, the policy is configured to allow all container images to be deployed.

Binary Authorization allows you to export and import a policy file in YAML format. This format reflects the structure of a policy as it is stored by the service. When you configure a policy using gcloud commands, you edit this file.

To view the default policy, export the policy YAML file:

gcloud container binauthz policy export

By default, the file has the following contents:

admissionWhitelistPatterns:
- namePattern: gcr.io/google_containers/*
- namePattern: gcr.io/google-containers/*
- namePattern: k8s.gcr.io/**
- namePattern: gke.gcr.io/**
- namePattern: gcr.io/stackdriver-agents/*
globalPolicyEvaluationMode: ENABLE
defaultAdmissionRule:
  evaluationMode: ALWAYS_ALLOW
  enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG
name: projects/${PROJECT_ID}/policy

Note: It is not necessary to use admissionWhitelistPatterns to allowlist Google-managed system images, as shown above. By default, globalPolicyEvaluationMode is set to ENABLE. This permits all Google-managed system images.

Here, the default rule is defined in the defaultAdmissionRule node. evaluationMode specifies that the policy allows all attempts at image deployment. In this tutorial, you update the default rule to require attestations.

For more information on the structure of a policy, see the Policy YAML Reference.

Create an attestor

An attestor is the verification authority that the Binary Authorization enforcer uses at deploy time to decide whether to allow GKE to deploy the corresponding signed container image. The attestor contains the public key and is typically managed by personnel in your organization who are responsible for software supply chain security.

Creating an attestor requires you to:

• Create a note in Container Analysis to store trusted metadata used in the authorization process
• Create the attestor itself in Binary Authorization and associate the note you created

For this tutorial, you have one attestor named test-attestor and a Container Analysis note named test-attestor-note. In a real-world scenario, you can have any number of attestors, each one representing a party that participates in the authorization process for a container image.

Create the Container Analysis note

1. Set variables that store the name of your attestor and Container Analysis note:

   ATTESTOR_NAME=test-attestor
   NOTE_ID=test-attestor-note
   

   Replace:

   • test-attestor: attestor name of your choice.
   • attestor-note: attestor note name of your choice.

2. Create a JSON file in /tmp/note_payload.json that describes the Container Analysis note:

   cat > /tmp/note_payload.json << EOM
   {
     "name": "projects/${PROJECT_ID}/notes/${NOTE_ID}",
     "attestation": {
       "hint": {
         "human_readable_name": "Attestor Note"
       }
     }
   }
   EOM
   

3. Create the note by sending an HTTP request to the Container Analysis REST API:

   curl -X POST \
       -H "Content-Type: application/json" \
       -H "Authorization: Bearer $(gcloud auth print-access-token)"  \
       --data-binary @/tmp/note_payload.json  \
       "https://containeranalysis.googleapis.com/v1/projects/${PROJECT_ID}/notes/?noteId=${NOTE_ID}"
   

4. Verify that the note was created:

   curl \
   -H "Authorization: Bearer $(gcloud auth print-access-token)" \
   "https://containeranalysis.googleapis.com/v1/projects/${PROJECT_ID}/notes/${NOTE_ID}"
   

Create the attestor

Now, you can create the attestor:

1. Create the attestor in Binary Authorization:

   gcloud container binauthz attestors create ${ATTESTOR_NAME} \
   --attestation-authority-note=${NOTE_ID} \
   --attestation-authority-note-project=${PROJECT_ID}
   

2. Verify that the attestor was created:

   gcloud container binauthz attestors list
   

The attestor you created is not yet usable without an associated PKIX key pair, which you create below.

For a multi-project configuration, you must set permissions on the Container Analysis note as described in Multi-Project Setup. This is not required in a single-project scenario, because the project has the required roles/containeranalysis.notes.occurrences.viewer by default.

Generate a key pair

Binary Authorization uses cryptographic keys to securely verify the identity of signers. This ensures that only authorized container images can be deployed. The key pair consists of a private key and a public key. The signer uses the private key to sign the container image digest, producing a signature that is then stored in an attestation. The public key is stored in the attestor. At deploy time, the Binary Authorization enforcer uses the attestor's public key to verify the signature in the attestation before allowing the container to deploy.

In this tutorial, you use Public-Key Infrastructure (X.509) (PKIX) format for cryptographic keys. This tutorial uses the recommended Elliptic Curve Digital Signing Algorithm (ECDSA) to generate a PKIX key pair. You can also use RSA or PGP keys for signing.

Key purposes and algorithms for more information on signing algorithms.

The keys generated and stored by Cloud Key Management Service (Cloud KMS) are PKIX-compliant. See Creating attestors using the gcloud CLI for more information on using PKIX keys and Cloud KMS.

To generate a PKIX key pair, follow these steps:

1. Create the private key:

   PRIVATE_KEY_FILE="/tmp/ec_private.pem"
   openssl ecparam -genkey -name prime256v1 -noout -out ${PRIVATE_KEY_FILE}
   

2. Extract the public key from the private key:

   PUBLIC_KEY_FILE="/tmp/ec_public.pem"
   openssl ec -in ${PRIVATE_KEY_FILE} -pubout -out ${PUBLIC_KEY_FILE}
   

3. Add the ECDSA public key to the attestor.

   Now, add the public key you exported to the attestor so that it can be used by Binary Authorization for identity verification:

   gcloud --project="${PROJECT_ID}" \
       beta container binauthz attestors public-keys add \
       --attestor="${ATTESTOR_NAME}" \
       --pkix-public-key-file=${PUBLIC_KEY_FILE} \
       --pkix-public-key-algorithm=ecdsa-p256-sha256
   

   Note: This command outputs the PUBLIC_KEY_ID you will use when creating an attestation. It is in the id field of the output and looks likeni:///sha-256;ybf_gINTzsBKLCaRIeQnExNhKFkGONXXXlr63QeZY-Q.

4. Save the public key ID.

   To save the public key ID, you can copy it from the output of public-keys add above. To view your attestor's public key ID after adding it to the attestor, use gcloud container binauthz attestors describe ${ATTESTOR_NAME}:

   PUBLIC_KEY_ID=$(gcloud container binauthz attestors describe ${ATTESTOR_NAME} \
     --format='value(userOwnedGrafeasNote.publicKeys[0].id)')
   

Configure the policy

Now, you can configure your policy. In this step, you export the policy YAML file to your local system and modify the default rule so that it requires an attestation by the attestor you defined above.

To configure the policy, follow these steps:

1. Create a new policy file that allows Google-maintained system images, sets the evaluationMode to REQUIRE_ATTESTATION, and adds a node named requireAttestationsBy that references the attestor you created:

   cat > /tmp/policy.yaml << EOM
       globalPolicyEvaluationMode: ENABLE
       defaultAdmissionRule:
         evaluationMode: REQUIRE_ATTESTATION
         enforcementMode: ENFORCED_BLOCK_AND_AUDIT_LOG
         requireAttestationsBy:
           - projects/${PROJECT_ID}/attestors/${ATTESTOR_NAME}
       name: projects/${PROJECT_ID}/policy
   EOM
   

2. Import the policy YAML file into Binary Authorization:

   gcloud container binauthz policy import /tmp/policy.yaml
   

Note: It can take a few minutes for the policy to take effect.

For more information on configuring a policy, see Configure a policy using the gcloud CLI.

Test the policy

You can test the policy you configured above by trying to deploy a sample container image to the cluster. The policy will block deployment because the required attestation has not been made.

For this tutorial, you can use sample images from Container Registry and Artifact Registry. The image from Container Registry is located at the path gcr.io/google-samples/hello-app:1.0. The image from Artifact Registry is located at the path us-docker.pkg.dev/google-samples/containers/gke/hello-app:1.0. Both paths contain public image created by Google that contains a "Hello, World!" sample. application.

First, try to deploy the image:

kubectl run hello-server --image gcr.io/google-samples/hello-app:1.0 --port 8080

Now, verify that the deployment was blocked by Binary Authorization:

kubectl get pods

The command prints the following message, which indicates that the image was not deployed:

No resources found.

You can get further details about the deployment:

kubectl get event --template \
'{{range.items}}{{"\033[0;36m"}}{{.reason}}:{{"\033[0m"}}\{{.message}}{{"\n"}}{{end}}'

You see a response that resembles the following:

FailedCreate: Error creating: pods POD_NAME is forbidden: admission webhook "imagepolicywebhook.image-policy.k8s.io" denied the request: Image IMAGE_NAME denied by Binary Authorization default admission rule. Image IMAGE_NAME denied by attestor ATTESTOR_NAME: No attestations found

In this output:

• POD_NAME: the name of the Pod.
• IMAGE_NAME: the name of the image.
• ATTESTOR_NAME: the name of the attestor.

Make sure to delete the deployment so you can continue to the next step:

kubectl delete deployment hello-server

Create an attestation

An attestation is a digital document created by a signer that certifies that GKE is allowed to deploy the associated container image. The process of creating an attestation is sometimes called "signing an image." A signer can be a person or, more often, an automated process that runs when a container image is built. The signature is created using the private key from a key pair. At deploy time, the Binary Authorization enforcer uses the attestor's public key to verify the signature in the attestation.

In this tutorial, your attestation simply states that you authorize the image for deployment.

To create an attestation, follow these steps:

1. Set variables that store the registry path and digest of the image:

   Container Registry

   IMAGE_PATH="gcr.io/google-samples/hello-app"
   IMAGE_DIGEST="sha256:c62ead5b8c15c231f9e786250b07909daf6c266d0fcddd93fea882eb722c3be4"
   IMAGE_TO_ATTEST=${IMAGE_PATH}@${IMAGE_DIGEST}
   

   Artifact Registry

   IMAGE_PATH="us-docker.pkg.dev/google-samples/containers/gke/hello-app"
   IMAGE_DIGEST="sha256:37e5287945774f27b418ce567cd77f4bbc9ef44a1bcd1a2312369f31f9cce567"
   IMAGE_TO_ATTEST=${IMAGE_PATH}@${IMAGE_DIGEST}
   

2. Generate the attestation payload:

   Note: In the following command, while an ${IMAGE_PATH} is required to create the signature payload for the attestation, only the ${IMAGE_DIGEST} is used at deploy time. This means you can deploy an identical container image from multiple locations with the same attestation.

   gcloud container binauthz create-signature-payload \
   --artifact-url=${IMAGE_TO_ATTEST} > /tmp/generated_payload.json
   

   The payload JSON file has the following contents:

   {
     "critical": {
       "identity": {
         "docker-reference": "gcr.io/google-samples/hello-app"
       },
       "image": {
         "docker-manifest-digest": "sha256:c62ead5b8c15c231f9e786250b07909daf6c266d0fcddd93fea
   882eb722c3be4"
       },
       "type": "Google cloud binauthz container signature"
     }
   }
   

3. Sign the payload with your PKIX private key and output a signature file:

   openssl dgst -sha256 -sign ${PRIVATE_KEY_FILE} /tmp/generated_payload.json > /tmp/ec_signature
   

   The signature file is a digitally-signed version of the payload JSON file you created above.

4. Create and validate the attestation:

   gcloud container binauthz attestations create \
       --project="${PROJECT_ID}" \
       --artifact-url="${IMAGE_TO_ATTEST}" \
       --attestor="projects/${PROJECT_ID}/attestors/${ATTESTOR_NAME}" \
       --signature-file=/tmp/ec_signature \
       --public-key-id="${PUBLIC_KEY_ID}" \
       --validate
   

   where PUBLIC_KEY_ID is the public key id that you found in Generate a PKIX key pair above.

   The validate flag checks that the attestation can be verified by the attestor you configured in your policy.

5. Verify that the attestation was created:

   gcloud container binauthz attestations list \
       --attestor=$ATTESTOR_NAME --attestor-project=$PROJECT_ID
   

For more information on creating attestations, see Creating Attestations.

Retest the policy

Again, test the policy by deploying a sample container image to the cluster. This time, you must deploy the image using the digest rather than a tag like 1.0 or latest, as Binary Authorization will use both the image path and digest to look up attestations. Here, Binary Authorization allows the image to be deployed because the required attestation has been made.

To deploy the image, follow these steps:

kubectl run hello-server --image ${IMAGE_TO_ATTEST} --port 8080

To verify that the image was deployed:

kubectl get pods

The command prints a message similar to the following, which indicates that deployment was successful:

NAME                            READY     STATUS    RESTARTS   AGE
hello-server-579859fb5b-h2k8s   1/1       Running   0          1m

Clean up

To avoid incurring charges to your Google Cloud account for the resources used in this tutorial, either delete the project that contains the resources, or keep the project and delete the individual resources.

Delete the cluster that you created in GKE:

gcloud container clusters delete \
    --zone=us-central1-a \
    test-cluster

What's next

• Learn more about Binary Authorization
• Learn key concepts used in Binary Authorization
• Use the built-by-cloud-build attestor to deploy only images built by Cloud Build (Preview).
• Enable dry run mode to disable enforcement
• Use breakglass to bypass enforcement