artomator

artomator (aka Artifact Registry Automator) automates the creation of Software Bill of Materials (SBOM) with Binary Authorization attestation for container images in Artifact Registry (AR). artomator will automatically add SBOM attestations to any image pushed to registry with the artomator-sbom label.

docker build -t $TAG --label artomator-sbom=spdx .

The value of the label dictates SBOM format. The two supported formats are cyclonedx and spdx). artomator also creates Binary Authorization attestation to support project or cluster levels policies.

how it works

1. Whenever an image is published to the Artifact Registry
2. A registry event is automatically published onto PubSub topic named gcr
3. PubSub subscription pushes that event to artomator service in Cloud Run with operation type and the image digest
4. If the operation type is INSERT, the artomator service retrieves metadata for that image from registry and check its labels
5. If the image includes artomator-sbom label, the service signs that image using KMS key
6. And creates new attestation based on the type of the label to the image in the registry (e.g. spdx)
7. If GCS bucket is configured, artomator will also save the generated artifacts to that bucket
8. On successful completion, artomator also creates Binary Authorization attestation using artomator-attestor with associated KMS key
9. Finally artomator also stores the processed image digests in a Redis store to avoid re-processing the same image again

Technically, adding attestation to an image creates yet another event, and could cause recursion. To prevent this and to allow artomator to scale to multiple instances the Redis-based cache is used which caches the processed digests for 72 hrs.

To processes images, artomator uses a few open source projects:

• cosign for image signing and verification
• syft for SBOM generation
• trivy for vulnerability scans
• jq for JSON operations

artifacts

In addition to attaching attestations to image in Artifact Registry and the Binary Authorization note, artomator also saves all the generated reports in GCS bucket (for example sbom.json). To make these names predictable, artomator prefixes them with the image SHA. For example, if the image digest is:

us-west1-docker.pkg.dev/s3cme1/artomator/tester@sha256:acaccb6c8f975ee7df7f46468fae28fb5014cf02c2835d2dc37bf6961e648838

then the list of artifacts in the registry for that image will be:

• acaccb6c8f975ee7df7f46468fae28fb5014cf02c2835d2dc37bf6961e648838-sbom.json
• acaccb6c8f975ee7df7f46468fae28fb5014cf02c2835d2dc37bf6961e648838-meta.json

where:

• -sbom.json is SPDX 2.3 formatted SBOM file
• -meta.json is the image metadata in the registry as it was when the image was processed

deployment

The prerequisites to deploy artomator include:

• Terraform CLI
• GCP Project
• gcloud CLI

To deploy the prebuilt artomator, first clone this repo:

git clone git@github.com:mchmarny/artomator.git

Then navigate to the deployment directory inside of that cloned repo:

cd artomator/deployment

Next, authenticate to GCP:

gcloud auth application-default login

Initialize Terraform:

terraform init

Note, this flow uses the default, local terraform state. Make sure you do not check the state files into your source control (see .gitignore), or consider using persistent state provider like GCS.

When done, apply the Terraform configuration:

terraform apply

When promoted, provide requested variables:

• project_id is the GCP project ID (not the name)
• location is GCP region to deploy to

When completed, this will output the configured resource information.

test deployment

To test the deployed artomator, use any valid Dockerfile you already have:

docker build -t $TEST_IMAGE_TAG --label artomator-sbom=spdx .
docker push $TEST_IMAGE_TAG

cleanup

To clean all the resources provisioned by this setup run:

terraform destroy

Note, this does not remove the created KMS resources.

disclaimer

This is my personal project and it does not represent my employer. While I do my best to ensure that everything works, I take no responsibility for issues caused by this code.