A controller includes: a communication port and a connection port that allow communication with another controller; and a hardware processor coupled to the ports. The hardware processor is configured to: transmit a first state signal indicating a state of the controller of an own device to the other controller from each port; receive a second state signal indicating a state of the other controller from the other controller via each of the ports; and switch, when the own device is in a standby state, the own device from the standby state to an operating state, when a breakdown of the other controller indicated by the received second state signal and an unreceived state in which the second state signal is not received for a predetermined time or more from both the communication and connection ports are monitored and at least one of the breakdown and the unreceived state is detected.

Methods and Nodes for Controlling a Physical Entity A method (100) is disclosed for controlling a physical entity. The method is performed by a controller node running at least two instances of a logical control function. The method comprises receiving over an input mechanism node input data relating to the physical entity (110) and providing, to each of the at least two instances of the control function, instance input data generated from the node input data. The method further comprises causing at least one of the instances to process the received instance input data and generate instance output data, and providing, over an output mechanism, instance output data from at least one of the instances of the control function, wherein the output mechanism is operably connected to the physical entity. The method further comprising synchronizing an internal state of each of the at least two instances of the control function.