[1][2][3] Appia is composed by a core that is used to compose protocols, and a set of protocols that provide group communication, ordering guaranties, atomic broadcast, among other properties.
The Appia core offers a clean way for the application to express inter-channel constraints.
This feature is obtained as an extension to the functionality provided by current systems.
Thus, Appia retains a flexible and modular design that allows communication stacks to be composed and reconfigured in run-time.
The existing protocols include interface with TCP and UDP sockets, virtual synchrony, several implementations of total order, causal order, among others.