Implementation of Raft consensus algorithm in GO

Overview

What is Raft?

Raft is a consensus algorithm that is designed to be easy to understand. It's equivalent to Paxos in fault-tolerance and performance. The difference is that it's decomposed into relatively independent subproblems, and it cleanly addresses all major pieces needed for practical systems. We hope Raft will make consensus available to a wider audience, and that this wider audience will be able to develop a variety of higher quality consensus-based systems than are available today. [Ref : The Raft Consensus Algorithm]

This package implements the Raft mechanism in GO language. Leveldb is used for underlying persistent log store requirement (github.com/cs733-iitb/log/). There are slight customizations from original Raft: In Search of an Understandable Consensus Algorithm specification. The read requests from clients are not redirected to a leader and they are not replicated. Any raft node can serve read requests regardless of their state.

Setup

# Requires libzmq3-dev library
go get github.com/cs733-iitb/log/...
go build raft_main.go

Run locally

go build
./cs733 -clean_start -config config.json -id 1 & 
./cs733 -clean_start -config config.json -id 2 & 
./cs733 -clean_start -config config.json -id 3 & 
./cs733 -clean_start -config config.json -id 4 & 
./cs733 -clean_start -config config.json -id 5 &

Note: Default log directory in config.json is /tmp/raft. Logs of this run will be stored in /tmp/raft/debug.log

Usage

Usage of raft_main:
  -clean_start
    	Whether to start raft in clean state. WARNING:This would delete all previous state and logs
  -config string
    	Path to config file (default "config.json")
  -id int
    	Id of this server (default -1)

Use sample_client program to communicate with the raft cluster.

Code Structure

The package is divided into different sub-packages.

Client Handler

Defines client handler class. Responsible for listening to client requests, replicate on raft nodes, apply replicated client requests to the file system and reply to client with response.

Raft Node

Raft node class. Responsible for inter-raftnode communication, serve client handler's replication requests, set raft timeouts, etc.

Raft State Machine

State machine class. Implements actual raft mechanism. Manages persistent replicated log, fullfills raft services according to raft state (leader, follower, candidate), generates actions for events, e.g. vote request action for timeout events, append request to followers for requests received from client, etc.

File System (fs) - A simple network file server

fs is a simple network file server. Access to the server is via a simple telnet compatible API. Each file has a version number, and the server keeps the latest version. There are four commands, to read, write, compare-and-swap and delete the file.

Refer assignment4>client_handler>filesystem>README.md for more information.

Logging mechanism

Raft logs are diveided into 4 levels, critical, error, warning and info.

Raft Config Structure

A univarsal config structure used by client handler, raft node, raft state machine and the client.

type Config struct {
    LogDir           string // Log file directory for this node
    ElectionTimeout  int
    HeartbeatTimeout int
    NumOfNodes       int
    ClusterConfig    cluster.Config
    ClientPorts      []int
    ServerList       []string
}

Sample config.json file

{
	"LogDir"            : "/home/raft/",
	"ElectionTimeout"   : 15000,    		# In msec
	"HeartbeatTimeout"  : 1000,     		# In msec
	"NumOfNodes"        : 5,
	"ClusterConfig"     : {
	                            "Peers"         : 
	                                   [{"Id":1,"Address":<IP:PORT of node 1>},
	                                    {"Id":2,"Address":<IP:PORT of node 2>},
                                    	{"Id":3,"Address":<IP:PORT of node 3>},
                                    	{"Id":4,"Address":<IP:PORT of node 4>},
                                    	{"Id":5,"Address":<IP:PORT of node 5>}],
	                            "InboxSize"     : 0,
	                            "OutboxSize"    : 0
	                        },
	                        
	# Port on which client handler will listen client requests
	"ClientPorts"       : [  0,
	                        <CLIENT_PORT of node 1>,
	                        <CLIENT_PORT of node 2>,
	                        <CLIENT_PORT of node 3>,
	                        <CLIENT_PORT of node 4>,
	                        <CLIENT_PORT of node 5>], 
	"ServerList"        : [
	                        "",
                        	<IP:CLIENT_PORT of node 1>,
                        	<IP:CLIENT_PORT of node 2>,
                        	<IP:CLIENT_PORT of node 3>,
                        	<IP:CLIENT_PORT of node 4>,
                        	<IP:CLIENT_PORT of node 5>,
                            ]
}

Client package

Client package for encoding and decoding file system requests response sent over TCP connection. A simple command line client program sample_client.go uses this Client class to communicate to server. sample_client.go can be used for testing purpose.

Version

1.0.0

Contact

• Developer : Abhishek Ghogare