@Override
    public ListInstancesResult listInstances(ListInstancesRequest request) {
        request = beforeClientExecution(request);
        return executeListInstances(request);
    }
<p>
Provides information for all active Amazon EC2 instances and Amazon EC2 instances terminated in the last 30 days,
up to a maximum of 2,000. Amazon EC2 instances in any of the following states are considered active:
AWAITING_FULFILLMENT, PROVISIONING, BOOTSTRAPPING, RUNNING.
</p>

@param listInstancesRequest
       This input determines which instances to list.
@return Result of the ListInstances operation returned by the service.
@throws InternalServerException
        This exception occurs when there is an internal failure in the Amazon EMR service.
@throws InvalidRequestException
        This exception occurs when there is something wrong with user input.
@sample AmazonElasticMapReduce.ListInstances
@see <a href="http://docs.aws.amazon.com/goto/WebAPI/elasticmapreduce-2009-03-31/ListInstances" target="_top">AWS
     API Documentation</a>
aws-java-sdk-emr/src/main/java/com/amazonaws/services/elasticmapreduce/AmazonElasticMapReduceClient.java