6.033 | Raft

For this recitation, you'll be reading In Search of an Understandable Consensus Algorithm. This paper describes Raft, an algorithm for achieving distributed consensus. The paper contrasts Raft to an algorithm called Paxos: you do not need to know anything about Paxos to read this paper. Raft was designed to be more understandable than Paxos.

This is a dense paper! As a result, we're going to spend two recitations on it. In the first recitation (this one), we will focus only on how the protocol works. You don't need to prepare for any broader discussion about Raft. It is okay—expected, even—for you to come to recitation with lots of questions about how Raft works.

Before reading the paper, check out two very helpful websites, which have some useful visualizations:

An introduction to distributed consensus
A visualization of Raft

With those visualizations in mind, read the paper. Skim sections 5.4.3, 7, 9.1, and 9.2.

The first four sections give background and motivation for Raft. Sections five and six are the primary technical sections.
Fig. 2 is a good reference to come back to after you've read the paper. Don't get stuck trying to memorize the entire table before you move onto page 5 of the paper; skip it, come back to it during your reading or at the end.

Question for Recitation

Before you come to this recitation, you'll turn in a brief answer to the following questions (really—we don't need more than a sentence or so for each question). Your TA will be in touch about exactly how to turn that in.

Your answers to these questions should be in your own words, not direct quotations from the paper.

In Raft, what is the leader's function?
How does the leader work?
Why does Raft need a leader?

As always, there are multiple correct answers for each of these questions.