@Override
  public RoleCommandOrder getRoleCommandOrder(Long clusterId) {
    Cluster cluster = null;
    try {
      cluster = clusters.getCluster(clusterId);
      return getRoleCommandOrder(cluster);
    } catch (AmbariException e) {
      return null;
    }

  }
RoleCommandOrderProvider which caches RoleCommandOrder objects for a cluster to avoid the cost of construction of
RoleCommandOrder objects each time.
ambari-server/src/main/java/org/apache/ambari/server/metadata/CachedRoleCommandOrderProvider.java