Requests a reboot of one or more instances. This operation is asynchronous; it only queues a request to reboot the specified instances. The operation succeeds if the instances are valid and belong to you. Requests to reboot terminated instances are ignored.
If an instance does not cleanly shut down within four minutes, Amazon EC2 performs a hard reboot.
For more information about troubleshooting, see Getting Console Output and Rebooting Instances (http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/instance-console.html) in the Amazon Elastic Compute Cloud User Guide.