ClusterIssuers are a resource type similar to Issuers. They are specified in exactly the same way, but they do not belong to a single namespace and can be referenced by Certificate resources from multiple different namespaces.
They are particularly useful when you want to provide the ability to obtain certificates from a central authority (e.g. Letsencrypt, or your internal CA) and you run single-tenant clusters.
The docs for Issuer resources apply equally to ClusterIssuers.
You can specify a ClusterIssuer resource by changing the
kind attribute of
an Issuer to
ClusterIssuer, and removing the
apiVersion: certmanager.k8s.io/v1alpha1 kind: ClusterIssuer metadata: name: letsencrypt-prod spec: ...
We can then reference a ClusterIssuer from a Certificate resource by setting
spec.issuerRef.kind field to ClusterIssuer:
apiVersion: certmanager.k8s.io/v1alpha1 kind: Certificate metadata: name: my-certificate namespace: my-namespace spec: secretName: my-certificate-secret issuerRef: name: letsencrypt-prod kind: ClusterIssuer ...
For more information on configuring Issuer resources, see the Issuers reference documentation.