In many scenarios, it's necessary to migrate or restore a gateway to a separate server. For example, a gateway may have initially been installed on a server with insufficient resources to support the current workload. In other cases, a hardware failure may have occurred on a gateway's server and thus it's necessary to quickly restore connectivity. Via the recovery key that's created when a gateway is first installed and configured, the data sources and their associated settings (authentication and credentials) can be restored on a new gateway machine. 

In the following image, the gateway installation application (PowerBIGatewayInstaller.exe) provides the option to Migrate, restore, or takeover an existing gateway rather than register a new gateway:

Choosing to Migrate, restore, or takeover an existing gateway will require the recovery key that is created when a gateway is originally configured. If this key is not available, the only option will be to install a new gateway and manually add the data sources and authorized users for that gateway. Additionally, only an administrator of a gateway can use the recovery key to restore a gateway to a different server.