README.md

Raft In Python

This is a work-in-progress attempt to implement Raft in Python. This codebase represents a personal exploration of the problem of Raft, so it's not intended as a model or complete implementation.

Inspiration for this project has come from the original Raft paper. This project uses the following Python libraries:

• trio
• rich

Running

You can install dependencies with poetry:

$ poetry install

After that, to run this using the provided ini file, you can invoke it using a node-id from 1 to 5:

$ python -m raft -c raft.ini -n 2
[04/07/22 07:09:33] WARNING  [AsyncRuntime -     aio.py:312
                             Follower] Starting
                             up now
                    INFO     [AsyncEventControll aio.py:113
                             er] Start: process
                             inbound messages
                    WARNING  [AsyncRuntime -     aio.py:287
                             Follower]: event
                             handler processing
                             started
                    INFO     SocketSe transport_async.py:68
                             rver
                             Start: l
                             istening
                              at 127.
                             0.0.1:31
                             11
                    INFO     [AsyncRuntime -     aio.py:242
                             Follower]
                             Converting to
                             Follower
                    INFO     [AsyncRuntime -     aio.py:223
                             Follower] resetting
                             election timer
                    INFO     [AsyncRuntime -     aio.py:268
                             Follower] Handling
                             event: EventType=Co
                             nversionToFollower
                             MsgType=none
                    INFO     [Clock.4439667616  clock.py:98
                             - ElectionTimeoutS
                             tartElection]
                             starting up with
                             interval 21.273
^C[04/07/22 07:09:34] WARNING  SHUTTING DOWN   __main__.py:57
                    WARNING  PLEASE WAIT FOR __main__.py:58
                             FULL STOP
                    WARNING  [AsyncRuntime -     aio.py:317
                             Follower] Shutting
                             down now

By default, the AsyncRuntime will be used, but there is also a ThreadedRuntime provided:

$ python -m raft -c raft.ini -n 2 -r ThreadedRuntime
[04/07/22 07:11:23] WARNING  [ThreadedRuntime - Follower] is     threaded.py:293
                             starting in DEBUG mode
                    WARNING  [ThreadedRuntime - Follower] will   threaded.py:294
                             run in the foreground
                    INFO     [ThreadedEventController] Start:     threaded.py:84
                             process inbound messages
                    INFO     [ThreadedEventController] Start:    threaded.py:103
                             process outbound messages
                    WARNING  [ThreadedRuntime - Follower] Start: threaded.py:268
                             primary event handler
                    INFO     [ThreadedRuntime - Follower]        threaded.py:224
                             Converting to Follower
                    INFO     [ThreadedRuntime - Follower]        threaded.py:206
                             resetting election timer
                    INFO     [Clock.4403522688 -                     clock.py:53
                             ElectionTimeoutStartElection] starting
                             up with interval 12.245
                    INFO     [ThreadedRuntime - Follower]        threaded.py:250
                             Handling event:
                             EventType=ConversionToFollower
                             MsgType=none
^C                    WARNING  SHUTTING DOWN                        __main__.py:57
                    WARNING  PLEASE WAIT FOR FULL STOP            __main__.py:58
                    INFO     [Clock.4403522688 -                     clock.py:57
                             ElectionTimeoutStartElection] is
                             shutting down
                    INFO     [ThreadedEventController] Stop:     threaded.py:115
                             process outbound messages

Note: At this time the AsyncRuntime is better with resources and easier to shutdown, so it's preferred over the ThreadedRuntime.

You can simultaneously run raft nodes in other terminals. If you have enough for quorum, one of these will be elected leader. Here's scree shot of five terminal sessions where a Leader is sending heartbeats to the other nodes in the cluster:

To send requests into the cluster see the examples in shell.py.

Design

This codebase splits up the Raft protocol into a few important pieces

• Socket Server (for receiving requests)
• Runtime
  • Event Controller
  • Event Handler
• Server
• Storage
• Clocks

This diagram may help:

The event controller and event handler use queues or channels to coordinate behavior between the socket server and the clocks that a Raft node may need to run.

To Do

This is a work-in-progress built for learning, so there are many things left to do:

• Tests
• Log Storage on Disk
• Snapshot cluster state on Disk
• More efficient message-serialization
• Try other transports and messaging-patterns instead of raw sockets (ZeroMQ and/or fanout, for instance)
• Allow nodes to join or leave cluster
• Construct database or reuse existing