Open/R generalizes the concept of a replicated state database found in well-known link-state routing protocols such as OSPF and ISIS. It uses this as an underlying message system upon which is used to build multiple applications. Distributed routing is just one of the applications that leverages this message bus. Facebook is leveraging Thrift for all message encoding and use the well-documented and mature open source ZeroMQ library for all message exchange, whether it’s intra-process or inter-process.

ZeroMQ typically uses TCP to establish transport connections and allows for flexible message patterns (with PUB/SUB being one important example) that we actively leverage. While it might sound heavyweight compared with OSPF and ISIS, which use their own “lightweight” transports, we haven’t found this to be an issue in modern networking hardware, such as the devices we use for Terragraph or the Wedge and 6-pack boxes running FBOSS in our data center networks. On the plus side, using ZeroMQ saves a lot of work implementing and testing the low-level aspects of the system, and it allows us to use the same framework for intra-application and inter-application messaging.