Requests a reboot of the specified 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 a few minutes, Amazon EC2 performs a hard reboot.

For more information about troubleshooting, see Troubleshoot an unreachable instance in the Amazon EC2 User Guide.