The default API server certificate is issued by an internal Azure Red Hat OpenShift cluster CA. Clients outside of the cluster will not be able to verify the API server’s certificate by default. This certificate can be replaced by one that is issued by a CA that clients trust.

Add an API server named certificate

The default API server certificate is issued by an internal Azure Red Hat OpenShift cluster CA. You can add additional certificates to the API server to send based on the client’s requested URL, such as when a reverse proxy or load balancer is used.

Prerequisites
  • You must have the certificate and key, in the PEM format, for the client’s URL.

  • The certificate must be issued for the URL used by the client to reach the API server.

  • The certificate must have the subjectAltName extension for the URL.

  • If a certificate chain is required to certify the server certificate, then the certificate chain must be appended to the server certificate. Certificate files must be Base64 PEM-encoded and typically have a .crt or .pem extension. For example:

    $ cat server_cert.pem int2ca_cert.pem int1ca_cert.pem rootca_cert.pem>combined_cert.pem

    When combining certificates, the order of the certificates is important. Each following certificate must directly certify the certificate preceding it, for example:

    1. Azure Red Hat OpenShift master host server certificate.

    2. Intermediate CA certificate that certifies the server certificate.

    3. Root CA certificate that certifies the intermediate CA certificate.

Do not provide a named certificate for the internal load balancer (host name api-int.<cluster_name>.<base_domain>). Doing so will leave your cluster in a degraded state.

Procedure
  1. Create a secret that contains the certificate and key in the openshift-config namespace.

    $ oc create secret tls <certificate> \(1)
         --cert=</path/to/cert.crt> \(2)
         --key=</path/to/cert.key> \(3)
         -n openshift-config
    1 <certificate> is the name of the secret that will contain the certificate.
    2 </path/to/cert.crt> is the path to the certificate on your local file system.
    3 </path/to/cert.key> is the path to the private key associated with this certificate.
  2. Update the API server to reference the created secret.

    $ oc patch apiserver cluster \
         --type=merge -p \
         '{"spec":{"servingCerts": {"namedCertificates":
         [{"names": ["<hostname>"], (1)
         "servingCertificate": {"name": "<certificate>"}}]}}}' (2)
    1 Replace <hostname> with the hostname that the API server should provide the certificate for.
    2 Replace <certificate> with the name used for the secret in the previous step.
  3. Examine the apiserver/cluster object and confirm the secret is now referenced.

    $ oc get apiserver cluster -o yaml
    ...
    spec:
      servingCerts:
        namedCertificates:
        - names:
          - <hostname>
          servingCertificate:
            name: <certificate>
    ...