cert-manager has the concept of Certificates that define a desired x509 certificate which will be renewed and kept up to date. A Certificate is a namespaced resource that references an Issuer or ClusterIssuer that determine what will be honoring the certificate request.

When a Certificate is created, a corresponding CertificateRequest resource is created by cert-manager containing the encoded x509 certificate request, Issuer reference, and other options based upon the specification of the Certificate resource.

Here is one such example of a Certificate resource.

apiVersion: cert-manager.io/v1alpha2
kind: Certificate
  name: acme-crt
  secretName: acme-crt-secret
  - foo.example.com
  - bar.example.com
    name: letsencrypt-prod
    # We can reference ClusterIssuers by changing the kind here.
    # The default value is Issuer (i.e. a locally namespaced Issuer)
    kind: Issuer
    group: cert-manager.io

This Certificate will tell cert-manager to attempt to use the Issuer named letsencrypt-prod to obtain a certificate key pair for the foo.example.com and bar.example.com domains. If successful, the resulting key and certificate will be stored in a secret named acme-crt-secret with keys of tls.key and tls.crt respectively. This secret will live in the same namespace as the Certificate resource.

The dnsNames field specifies a list of Subject Alternative Names to be associated with the certificate.

The referenced Issuer must exist in the same namespace as the Certificate. A Certificate can alternatively reference a ClusterIssuer which is non-namespaced and so can be referenced from any namespace.

You can read more on how to configure your Certificate resources here.