Awesome

Jump Consisten Hash for luajit

A simple implementation of this paper.

Features

• small memory footprint and fast
• consistence is maintained through servers' updating

Installation

make
make PREFIX=/usr/local/openresty install

Usage

• you can use the basic jchash module to do consistent-hash

local jchash = require "resty.chash.jchash"

local buckets = 8
local id = jchash.hash_short_str("random key", buckets)

• or you can use the wrapping module resty.chash.server to consistent-hash a list of servers

local jchash_server = require "resty.chash.server"

local my_servers = {
    { "127.0.0.1", 80, 1},   -- {addr, port, weight} weight can be left out if it's 1
    { "127.0.0.2", 80 },
    { "127.0.0.3", 80 }
}

local cs, err = jchash_server.new(my_servers)
local uri = ngx.var.uri
local svr = cs:lookup(uri)
local addr = svr[1]
local port = svr[2]

-- now you can use the ngx.balancer to do some consistent LB

-- you can even update the servers list, and still maintain the consistence, eg.
local my_new_servers = {
    { "127.0.0.2", 80 },
    { "127.0.0.3", 80 },
    { "127.0.0.4", 80 }
}

cs:update_servers(my_new_servers)
svr = cs:lookup(uri)   -- if the server was 127.0.0.2, then it stays the same,
                       -- as we only update the 127.0.0.4.

-- what's more, consistence is maintained even the number of servers changes! eg.
local my_less_servers = {
    { "127.0.0.2", 80 },
    { "127.0.0.3", 80 }
}
cs:update_servers(my_less_servers)
svr = cs:lookup(uri)   -- if the server was 127.0.0.2, then it stays the same,
                       -- if the server was 127.0.0.4, then it has 50% chance to be
                       -- 127.0.0.2 or 127.0.0.3

cs:update_servers(my_new_servers)
svr = cs:lookup(uri)   -- if the server was 127.0.0.2, then it has 66% chance to stay the same

Todo

• weight for the servers list [done]
• Test::Nginx [done]

Test

make test