Kapitan generators as supply-chain artifacts

Kapitan's kadet generators are Python packages that turn an inventory into
Kubernetes manifests, Terraform JSON or anything else. They are also code
that runs on your machine and in CI with access to your inventory and
secrets. In most projects they get copied between repositories and run
without review.

kadet-hub is a community catalog that treats them
like any other dependency you would want to pin and verify. It lists 35
generators today, among them Argo CD, cert-manager, Cilium, CloudNativePG,
Crossplane, External Secrets, Flux, KEDA, Kyverno, the Prometheus operator,
Velero and Terraform generators for AWS, AzureRM, Google Cloud and Open
Telekom Cloud.

What a version goes through

Before a version is listed, a gate runs on the pull request that registers
it:

• secret, malware and code scans of the source;
• a compile of the generator's fixture targets in a gVisor sandbox without network, on every inventory backend it declares, once more with Kapitan's compile cache, which must produce identical output;
• validation of the rendered output against the JSON Schemas the generator ships;
• a server-side dry run of every built-in document, and of every custom resource whose CRD the generator ships, against a throwaway kube-apiserver.

A maintainer reviews the result. The version is then published to
ghcr.io/kadet-hub/<name> as an OCI artifact with a Sigstore signature,
an SBOM and a transparency log entry, and you pin it by digest in your
inventory.

What the gate caught

The dry runs were added after schema validation alone let real bugs
through. Some examples from the generators now listed:

• probes rendered as empty objects (startupProbe: {}), which the API server rejects and a JSON Schema accepts;
• a Flux HelmRelease with both chart and chartRef, which violates a CEL rule in the CRD that no JSON Schema check evaluates;
• a generator whose submodule cached the inventory of the first target it was imported for, so the output depended on the order in which Kapitan compiled targets. The cache comparison showed it as a namespace that differed between two runs of the same commit.

The CRD dry run has its own write-up:
Checking custom resources against their CRDs.
It also covers operators that create their CRDs at runtime and publish
no YAML, such as KubeVirt and CDI, which leaves nothing to validate
against offline.

Consuming and writing generators

The consumer guide
shows how to pull a generator with Kapitan's oci dependency type and
verify it. kapitan compile --fetch checks neither signatures nor
digests, so a reusable GitHub workflow does the verification and compiles
your inventory in the same sandbox.

To write one, start from the
generator template. Its
./check script runs the gate's scans and the sandboxed compile locally,
and Writing a Kapitan generator
documents the contract Kapitan gives a generator.

kadet-hub is a community project and is not affiliated with or endorsed by
the Kapitan project or kapicorp. Generator requests and feedback are
welcome as issues.

Originally published at kadet-hub.org.