[abronan]

I wrote the initial implementation of the raft subsystem and it was definitely not a copy/paste. We started from scratch (using etcd's core raft) with the transport layer being grpc. My initial experiment could be found in this repository [1]. I then took the code from my initial experiment and included this into Swarmkit [2]. From there we went through many iterations on the initial code base and improved the UI with Docker swarm `init`/`join`/`leave` to make the experience of managing the cluster "friendly".

We spent quite some time evaluating different raft and paxos implementations (mostly Consul and etcd raft libraries), and found out etcd to be the most stable and flexible for our use case. It was very easy for example to swap the transport layer to use grpc. The fact that etcd implementation is represented as a simple state machine makes it also much easier to reason about under complex scenarios for debugging purposes, instead of digging into multiple layers of abstractions.

In retrospect, this came with quite a learning curve. We've had to deal with issues caused by our own misunderstandings on how to use the library properly. At the same time the fact that the developers favored stability as opposed to user friendliness was exactly what we found attractive using etcd's raft. Additionally, CoreOS developers were super friendly and helpful to help us fix these issues. We've reported and fixed some bugs as well. Kudos to them for all the help they provided at the time.

[1] https://github.com/abronan/proton [2] https://github.com/docker/swarmkit/commit/89de50f2092dfd2170...

[bboreham]

I apologise for my misunderstanding.

What I remember is, during DockerCon in June 2016, I went into the code to see how it worked, and I found a top-level file setting up data structures and handlers that seemed to be 90% the same as the equivalent file in etcd. And the underlying implementation is reused via vendoring.

Maybe this rings a bell with you and you can tell me what I saw, because I can't find it now.

Maybe I dreamed the whole thing.

I did, and still do, think integrating etcd into Swarm Mode was a masterstroke; we had spent the previous two years working to avoid "first you must install etcd" in a different way that nobody got. Afterwards we created kubeadm to ape the 'init' and 'join' functionality.