code: @Override
      public DescribeFleetInstancesResult describeFleetInstances(DescribeFleetInstancesRequest request) {
          request = beforeClientExecution(request);
          return executeDescribeFleetInstances(request);
      }
docs: <p>
  Describes the running instances for the specified EC2 Fleet.
  </p>
  
  @param describeFleetInstancesRequest
  @return Result of the DescribeFleetInstances operation returned by the service.
  @sample AmazonEC2.DescribeFleetInstances
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/ec2-2016-11-15/DescribeFleetInstances" target="_top">AWS API
  Documentation</a>