Datadog Turnstile: Supply Chain Policy Beyond Image Signing
Enterprise Developer PlatformsA malicious commit, a poisoned dependency or a compromised build runner can all produce a container image with a perfectly valid signature. That gap is why Datadog built Turnstile, an internal system that checks what went into an artifact, not just whether it changed after signing. It runs in the deployment hot path across tens of thousands of deployments and images each day. For platform teams that stopped at image signing, it shows what the next layer looks like.
What Happened
In a Datadog engineering post, security engineering managers Callan Lamb and Brianna Heffernen describe Turnstile. It extends Datadog’s existing image signing, where a custom containerd plugin verifies signatures at pull time, by asking a broader question at deploy time: does this artifact meet the requirements for this environment?
Turnstile rests on three ideas: signed evidence for each meaningful event in an artifact’s life, policies scoped per environment, and progressive enforcement that can warn in some environments and block in others.
How It Works
Attestations. Each step produces a signed claim built on a modified version of in-toto, keyed so it links to the next stage. Datadog’s attestation types include:
| Attestation | What it proves |
|---|---|
| Commit safety | LLM scan found the commit benign, and it was signed with a trusted key |
| Source provenance | Repository, organization and governance controls at commit time |
| Pull request | Which PR merged it, whether it was reviewed, who approved |
| Build provenance | Pipeline, job, container digest and image signature |
| SBOM and vulnerability metadata | Dependencies and their known vulnerabilities at build time |
| Deployment | Kubernetes cluster and namespace |
Keyless signing. A library called dd-attest signs each attestation with an ephemeral key bound to a workload identity, such as a CI job or a Kubernetes service account backed by OIDC, instead of long-lived keys. If a CI job is compromised, every attestation it produced in that window can be invalidated.
Policy. Open Policy Agent evaluates Rego policies against the attestations, such as requiring an approved PR on a protected branch or an SBOM from the approved scanner with no known critical vulnerability. Each evaluation produces a signed verification summary that deployment UIs, compliance reports and incident response can reuse without re-running the check. The policies themselves are distributed through The Update Framework, since a tampered policy could quietly let a bad artifact through.
What This Means for Platform Teams
Most of Turnstile is built from open standards, including the SLSA threat model, in-toto, OPA and TUF, so the pattern can be copied without Datadog’s code. Datadog introduces new policies in audit mode first to find pipeline gaps and false positives before enforcing them. The commit-safety check relies on the LLM malicious-code scanning covered in Stack Archive’s look at Datadog’s BewAIre.
The So What
Platform teams that already sign images should start by recording build provenance and PR-approval attestations for production deploys, then write one OPA policy in audit mode that requires both. Move to keyless, identity-bound signing before adding more attestation producers, and decide early how the policies themselves will be signed and distributed.
Source: Datadog Engineering Blog
Content created with AI assistance and reviewed for accuracy.
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