New events on a chain are pushes to all nodes designated by the participating identities. Nodes may also request an event chain for instance when a user of the node is invited on a chain.
A message broker allows for asynchronous and decoupled data transfer. With a protocols like HTTP, an unresponsive node could slow down other nodes. With a message broker, messages to an unreachable node may be delivered as a later time.
Recommended message brokers
See this list of client and developer tools that support
HTTP REST API
Nodes MAY have an HTTP REST API which can be used to interface with the event chain service. Other node SHOULD NOT use the REST API. It's only intended for client applications hosted by the owner of the node.