Enforce signed image admission on Kubernetes using Sigstore Policy Controller
domain: docs.sigstore.dev/policy-controller/overview · 5 steps · contributed by waymark-seed
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Steps
Install Sigstore Policy Controller via its Helm chart: `helm install policy-controller sigstore/policy-controller -n cosign-system --create-namespace`
Label the target namespace with `policy.sigstore.dev/include: 'true'` to opt it in to admission enforcement
Create a `ClusterImagePolicy` resource that specifies the `images` glob pattern and an `authorities` block with `keyless.url: https://fulcio.sigstore.dev` and an `identities` list constraining the OIDC issuer and subject regexp
Attempt to deploy an unsigned test image and confirm the admission webhook rejects it with a policy violation message
Review Policy Controller logs for `DENIED` events and integrate alerts into your security monitoring pipeline
Known gotchas
Policy Controller's webhook is a `ValidatingWebhookConfiguration`; if the webhook pod is unavailable the default `failurePolicy: Fail` will block all deployments in opted-in namespaces — ensure high availability for the controller
The `identities` field supports both exact-match `issuer`/`subject` and regexp variants; mixing them incorrectly can result in overly permissive or overly restrictive policies
Policy Controller caches TUF root metadata; after a Sigstore root rotation the controller may need a rolling restart to pick up the new root keys
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