public KerberosDescriptor getKerberosDescriptorUpdates(Cluster cluster) {
    // find instance using name and foreign keys
    TreeMap<String, String> foreignKeys = new TreeMap<>();
    foreignKeys.put("cluster", String.valueOf(cluster.getClusterId()));

    ArtifactEntity entity = artifactDAO.findByNameAndForeignKeys("kerberos_descriptor", foreignKeys);
    return (entity == null) ? null : kerberosDescriptorFactory.createInstance(entity.getArtifactData());
  }
Get the user-supplied Kerberos descriptor from the set of cluster artifacts

@param cluster the cluster
@return a Kerberos descriptor
ambari-server/src/main/java/org/apache/ambari/server/controller/KerberosHelperImpl.java