Virtual Machine High Availability
High availability determines whether a virtual machine is automatically restarted when it is shut down for an unknown reason. If high availability is enabled and the virtual machine is manually shut it down from within a terminal session, the machine will automatically be restarted by Stratosphere. However, if you click on the "Stop" button on the Stratosphere portal interface, the machine will remain shut down. This will also apply to API calls using the stopVirtualMachine command.
The high availability setting can be set on a per machine basis.
To learn how to enable or disable High Availability, go HERE