Ryu comes with applications such as simple_switch, router, isolation, firewall, GRE tunnel, topology, and VLAN. It's applications are single-threaded entities which implement various functionalities in Ryu; they also send asynchronous events to each other.

Ryu applications consist of a receive queue for events, which is in a first in first out (FIFO) buffer architecture to keep the operation of events. Also, applications include a thread for processing events from this queue; events are released from the receive queue and the right event handler is called. The event handler is called within the context of the event-processing thread, which works in a way that once control is given to the handler, no other events for the Ryu application will be processed until control is returned.

The functional architecture of a Ryu application is shown as follows: