Serf is a service orchestration and management tool.

It offers a decentralized, lightweight, highly available and fault
tolerant solution for service discovery and orchestration that runs
on Linux, Mac OS-X and Windows.

An efficient and lightweight gossip protocol is used to communicate
among the nodes, and node failures are detected and notified to the rest
of the cluster. An event system is built on top of Serf, so that events
such as deploys, configuration changes, et.c, can be propagated around.
Serf is also completely masterless, meaning there's no single point of
failure.

This package provides the agent that should be started on every node.