@Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    sb.append("{" + " clusterName=").append(clusterName)
        .append(", clusterId=").append(clusterId)
        .append(", provisioningState=").append(provisioningState)
        .append(", securityType=").append(securityType)
        .append(", stackVersion=").append(stackVersion)
        .append(", desired_scv=").append(serviceConfigVersionRequest)
        .append(", hosts=[")
        .append(hostNames != null ? String.join(",", hostNames) : StringUtils.EMPTY)
        .append("] }");
    return sb.toString();
  }
Gets any configuration-based request (if any).
@return the list of configuration requests,
or <code>null</code> if none is set.
ambari-server/src/main/java/org/apache/ambari/server/controller/ClusterRequest.java