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jump-consistent-hash: Consistent hash for nginx-module-lua

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua-resty-jump-consistent-hash

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua5.1-resty-jump-consistent-hash

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-jump-consistent-hash v0.1.4 released on May 09 2016.

A simple implementation of this paper.

Features

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

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
                       -- 127.0.0.3 or 127.0.0.4

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

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-jump-consistent-hash.