ExRaft

An Elixir implementation of the raft consensus protocol.

This library takes an in-memory approach for storing log entries and the state machine state, therefore it is not really suitable for storing large amounts of data. Since it's in-memory only though, it's supposed to be fast.

To get started, check out the ExRaft.StateMachine documentation.

To understand the internals of the project, check out the main ExRaft module documentation.

For a full overview of the project, check out the full online documentation.

Installation

The package can be installed by adding ex_raft to your list of dependencies in mix.exs:

def deps do
  [
    {:ex_raft, "~> 0.2.0"}
  ]
end

Example

init_arg = [very_cool: true]
initial_config = [raft1: node(), raft2: node()]

# after starting these servers, they will time out and eventually elect a leader
# amongst themselves
{:ok, _} = ExRaft.start_server(YourStateMachine, init_arg, name: :raft1, initial_config: initial_config)
{:ok, _} = ExRaft.start_server(YourStateMachine, init_arg, name: :raft2, initial_config: initial_config)

# this server can never become leader unless its added to an existing cluster
# since it doesn't know of any other server but is required to achieve
# a minimum majority of 2 in elections and log replication
{:ok, _} = ExRaft.start_server(YourStateMachine, init_arg, name: :raft3, min_majority: 2)

# we could pick any server to await the leader
leader = ExRaft.await_leader(:raft1)
:ok = ExRaft.add_server(leader, :raft3)

# the success result of write/3 depends on the state machine
:ok = ExRaft.write(leader, :hello)

# making a write/3 call to a follower results in an error
follower = List.delete(initial_config, leader) |> List.first()
{:error, {:redirect, ^leader}} = ExRaft.write(follower, :hello)

# if we stop the active leader (or it crashes)
# the rest of the cluster will be able to recover
:ok = ExRaft.stop_server(leader)
:ok = ExRaft.trigger_election(:raft3)
new_leader = ExRaft.await_leader(:raft3)
true = Enum.member?([raft2: node(), raft3: node()], new_leader)

Contributing

All contributions must adhere to the guidelines below:

• https://github.com/christopheradams/elixir_style_guide
• https://github.com/christopheradams/elixir_style_guide#modules
• https://hexdocs.pm/elixir/master/library-guidelines.html
• https://hexdocs.pm/elixir/master/writing-documentation.html

License

ExRaft source code is released under Apache License 2.0. Check LICENSE file for more information.