How do you implement Tekton Chains for supply chain security and artifact signing?

Tekton Chains addresses one of the most critical challenges in modern software delivery: proving that a container image or artifact was actually built by your CI/CD system and has not been tampered with between build and deployment. In a world where supply chain attacks like SolarWinds and Codecov have compromised thousands of organizations, simply building an image is no longer sufficient. You must cryptographically prove who built it, what source code was used, what build steps were executed, and that the resulting artifact is identical to what was produced. Tekton Chains automates this entire provenance chain without requiring developers to modify their pipelines.

Tekton Chains operates as a Kubernetes controller that watches for completed TaskRuns and PipelineRuns. When the payments-api pipeline finishes building a container image, Chains automatically captures the build metadata including the git commit SHA, the Dockerfile used, the base image digest, and all input parameters. It then generates an in-toto attestation document conforming to the SLSA (Supply-chain Levels for Software Artifacts) framework. This attestation is cryptographically signed using either a locally stored key pair, a KMS-managed key from AWS KMS, GCP KMS, or HashiCorp Vault, or Sigstore's Fulcio for keyless signing where the identity is bound to an OIDC token from the Kubernetes service account. The signed attestation is then stored alongside the artifact in the OCI registry, attached as a cosign signature or uploaded to a Rekor transparency log for public verifiability.

In a production environment at enterprise scale, implementing Chains for the order-processing-service and inventory-sync pipelines requires careful architecture decisions. The signing key management strategy is paramount. Organizations handling financial transactions through their checkout-service typically use hardware-backed KMS keys with strict IAM policies, ensuring that only the Tekton Chains controller service account can access the signing key. The transparency log integration means every signed artifact is recorded in an immutable append-only ledger, making it impossible to retroactively modify or deny that a particular build occurred. For the user-auth-service, this creates a complete audit trail from git commit to running container that satisfies SOC 2, FedRAMP, and PCI-DSS compliance requirements without manual evidence collection.

The verification side of the equation is equally important. When ArgoCD or a Kubernetes admission controller like Kyverno or OPA Gatekeeper attempts to deploy the payments-api image, it first verifies the cosign signature and validates the SLSA attestation against organizational policies. These policies can enforce requirements such as the image was built from the main branch of an approved repository, the build pipeline included a security scanning step that passed, the source code had at least two approved reviewers, and the build occurred on a trusted build cluster. If any of these conditions fail verification, the deployment is blocked before the image ever reaches the production cluster. This creates a cryptographic trust chain from developer commit through CI/CD build to production deployment.

The operational complexity of Tekton Chains centers around key rotation, attestation format evolution, and multi-cluster deployment. Key rotation requires updating the signing key across all clusters while maintaining the ability to verify artifacts signed with the previous key during the rotation window. Organizations running the inventory-sync and checkout-service across multiple regions deploy Chains in each cluster with region-specific KMS keys, using a federated trust model where each regional key is registered as a trusted signer in the verification policies of all clusters. The SLSA framework defines four levels of assurance, and reaching SLSA Level 3 requires that the build platform itself is hardened, the build definition comes from a version-controlled source, and the provenance is non-falsifiable. Tekton Chains provides the provenance generation and signing infrastructure, but achieving SLSA Level 3 also requires securing the Tekton controller, isolating build namespaces, and ensuring that pipeline definitions cannot be modified at runtime.