Distkv

(Distributed Key Value)

Description

I made this simple project, based on https://github.com/mmmries/dkv repo, that uses https://github.com/lindenbaum/lbm_kv project to provides distributed key-value in-memory db for elixir project.

Based on https://github.com/mmmries/dkv project, you are required to LINK ALL NODES using sys.config file. Consequently, you must know your nodes and register it in sys.config file before you can start your app in many nodes.

This approach doesn't really suit my requirement, as I want to be able to start my app in 1 node then scalling horizontally as needed. So I want to be able to provide NODE NAME everytime I want to start my app in 2nd, 3rd node and so on.

So by following a simple trick from https://medium.com/@jmerriweather/elixir-phoenix-amnesia-multi-node-451e8565da1d project, I code my /config/config.exs like below:

use Mix.Config

# Takes JOIN_TO env variable provided by deployer (if any) on starting this app 
config :distkv, node_addr: System.get_env("JOIN_TO")

Then in /lib/application.ex, my start block codes is like below:

def start(_type, args) do
    # Read provided :node_addr from config.exs
    node_addr = Application.get_env(:distkv, :node_addr)

    import Supervisor.Spec, warn: false

    # Define workers and child supervisors to be supervised
    children = [
      # Starts DkvServer (GenServer) with node_addr as argument
      worker(Distkv.DkvServer, [node_addr]),
    ]

    # See http://elixir-lang.org/docs/stable/elixir/Supervisor.html
    # for other strategies and supported options
    opts = [strategy: :one_for_one, name: Distkv.Supervisor]
    Supervisor.start_link(children, opts)
  end

How Distkv.DkvServer (/lib/dkv_server.ex) magically initiates node connections then starts Mnesia replications with previously established Mnesia can be view in dkv_server.ex

Part of my code in dkv_server.ex came from this guy: @mmmries sample in here, thank him for that :) And thanks to lindenbaum team as well, for their great project :)

How to test this app

P.S. I'm using Windows OS here

Start 1st node

C:\> iex --name node_1@YOUR_IP --cookie freak -S mix run
iex(node_1@YOUR_IP)1> alias Distkv.DkvServer
iex(node_1@YOUR_IP)2> DkvServer.insert(:one, %{msg: "Hello World"})
:ok
iex(node_1@YOUR_IP)3> DkvServer.select_all
[%{msg: "Hello World"}]

Start 2nd node

C:\> set JOIN_TO=node_1@YOUR_IP
C:\> iex --name node_2@YOUR_IP --cookie freak -S mix run
iex(node_2@YOUR_IP)1> alias Distkv.DkvServer
iex(node_2@YOUR_IP)2> DkvServer.select_all
[%{msg: "Hello World"}]

That's it guys... good luck with your project, I hope this would help you somehow :D

Note

My steps in learning elixir haven't reach to any real production right now, so I cannot be sure whether this approach is possible outside development phase. If any of you know, please post an issue here. Thanks :D