code: @Override
      public DBCluster failoverDBCluster(FailoverDBClusterRequest request) {
          request = beforeClientExecution(request);
          return executeFailoverDBCluster(request);
      }
docs: <p>
  Forces a failover for a DB cluster.
  </p>
  <p>
  A failover for a DB cluster promotes one of the Read Replicas (read-only instances) in the DB cluster to be the
  primary instance (the cluster writer).
  </p>
  <p>
  Amazon Neptune will automatically fail over to a Read Replica, if one exists, when the primary instance fails.
  You can force a failover when you want to simulate a failure of a primary instance for testing. Because each
  instance in a DB cluster has its own endpoint address, you will need to clean up and re-establish any existing
  connections that use those endpoint addresses when the failover is complete.
  </p>
  
  @param failoverDBClusterRequest
  @return Result of the FailoverDBCluster operation returned by the service.
  @throws DBClusterNotFoundException
  <i>DBClusterIdentifier</i> does not refer to an existing DB cluster.
  @throws InvalidDBClusterStateException
  The DB cluster is not in a valid state.
  @throws InvalidDBInstanceStateException
  The specified DB instance is not in the <i>available</i> state.
  @sample AmazonNeptune.FailoverDBCluster
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/neptune-2014-10-31/FailoverDBCluster" target="_top">AWS API
  Documentation</a>