Peer-To-Peer Publish/Subscribe with ZeroMQ

The presence of a broker can considerably simplify the architecture of a messaging system. However, in some circumstances, this might not be the best solution. This includes all the situations where a low latency is critically important, when scaling complex distributed systems, or when the presence of a single point of failure isn’t an option. The alternative to using a broker is, of course, implementing a peer-to-peer messaging system.

Introducing ZeroMQ

If our project is a good candidate for a peer-to-peer architecture, one of the best solutions to evaluate is certainly the ZeroMQ library(also known as zmq or ØMQ). ZeroMQ is a networking library that provides the basic tools to build a large variety of messaging patterns. It’s low-level, extremely fast, and has a minimalistic API, but it offers all the basic building blocks to create a solid messaging system, such as atomic messages, load balancing, queues, and many more. It supports many types of transport, such as in-process channels (inproc://), inter-process communication (ipc://), multicast using the PGM protocol (pgm:// or epgm://), and, of course, the classic TCP (tcp://).

Among the features of ZeroMQ, we can also find tools to implement a Publish/ Subscribe pattern, which is exactly what we need for our example. So, what we’re going to do now is remove the broker (Redis) from the architecture of our chat application and let the various nodes communicate in a peer-to-peer fashion, leveraging the publish/subscribe sockets of ZeroMQ.

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