A Raft implementation in Python, written as part of David Beazley's Raft course.
There's more to the course (smaller exercises to highlight key concepts, a key-value store layer), this is only my implementation of the core Raft algorithm following the paper.

I really enjoyed the week-long course. I recommend it and would probably take it again some time.

Writing Raft is challenging! Debugging and testing distributed systems is notoriously difficult, this is a good introduction as to why.

You can go in depth on many aspects of the implementation (networking, persistence, interfacing with clients...). My focus was on setting up simulation-based tests to spot typical concurrency bugs between Raft servers.

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I wrote this to experiment and learn. If you really want to run it:

• To test this manually, adjust configuration in raftconfig.py and launch:

  # in different terminals
  python console.py 1 leader
  python console.py 2 follower
  python console.py 3 follower
  

See console.py for available commands.

• Run tests with pytest.
  The test_simulated.py file uses simulation testing.
  I find it interesting to introduce subtle bugs and see if the tests can find them. Example: comment out this line (raftlogic.py:254):

  and (self.state.voted_for is None or self.state.voted_for == msg.candidate_id)
  

  This allows servers to vote for multiple candidates and hopefully causes the simulation tests (at least) to fail.