Caliopen is a complete scalable messaging platform. Many components interacts to complete all services and processes covered by this platform.
Scalability is merely achieved using data store with such capability, Cassandra for main storage, elasticsearch for indexing when it have to be done.
A specific code architecture is defined to make component responsabilities correctly isolated. Many protocols have to be covered and they aren’t related to an HTTP REST Api in some case.
You can refer to :