Raf

Overview

Raf is an Elixir implementation of the Raft distributed consensus protocol. It provides users with an api for building consistent (2F+1 CP), distributed state machines. Raft protocol is described in the original paper.

Features

• Leader election
• Log replication
• Configuration changes

Installation

If available in Hex, the package can be installed by adding raf to your list of dependencies in mix.exs:

def deps do
  [
    {:raf, "~> 0.1.0"}
  ]
end

Example

Launch 3 nodes

$ iex --sname peer1@localhost -S mix
iex(peer1@localhost)1> Raf.start_test_node(:peer1)

$ iex --sname peer2@localhost -S mix
iex(peer2@localhost)1> Raf.start_test_node(:peer2)

$ iex --sname peer3@localhost -S mix
iex(peer3@localhost)1> Raf.start_test_node(:peer3)

when peers have been running. You can check peers' status:

:sys.get_status(:peer1)
or
:sys.get_state(:peer1)

Config cluster

At this point all the peers are in the follow state. In order to get them to communicate we need to define a cluster configuration. In our case, we'll run on node peer1:

peers = [{:peer1, :peer1@localhost},
        {:peer2, :peer2@localhost},
        {:peer3, :peer3@localhost}]
Raf.set_config(:peer1, peers)

Once election is done. You can see who is the current leader:

iex(peer2@localhost)3> Raf.get_leader(:peer2)
{:peer1, :peer1@localhost}

Write Operations

# Create a new ets table
Raf.write(:peer1, {:new, :sometable})

# Store an erlang term in that table
Raf.write(:peer1, {:put, :sometable, :somekey, :someval})

# Delete a term from the table
Raf.write(:peer1, {:delete, :sometable, :somekey})

# Delete a table
Raf.write(:peer1, {:delete, :sometable})

Read Operations

# Read an erlang term
Raf.read(:peer1, {:get, :sometable, :somekey})

# list tables
Raf.read(:peer1, :list_tables)

# list keys
Raf.read(:peer1, {:list_keys, :somekey})