Are you sure flynn uses etcd for service discovery instead of its own[1]?
Looks like it uses Google Omega instead of RAFT which etcd uses.
https://github.com/flynn/discoverd
discoverd is an API on top of another system. Right now, Flynn uses discoverd backed by etcd, though they indicate that this could be replaced with Zookeeper, etc. due to the mdoular design.
As I understand it Google Omega and RAFT are two different things. Google Omega is Google's answer to Apache Mesos. Omega would need a service like Raft to understand what services are currently available. In short, Google Omega is not a service discovery service.
Actually, I think Google Omega is the next-generation scheduler after their original Borg scheduler, which in-turn inspired Mesos.
The design of Omega is quite different than Mesos. I really do recommend reading the Mesos & Omega papers, they are quite interesting.
And yes, Raft is a consensus algorithm for keeping a set of distributed state machines in a consistent state. Mesos actually uses ZooKeeper under the hood for master election, which uses its own consensus algorithm (ZAB - Zookeeper Atomic Broadcast).
