Citadel

Citadel is a ditribution based features lib.

Features

• Distributed process registry with groups support using Mnesia
• Nodes discovery through redis
• Distributed supervisor

Installation

def deps do
  [{:citadel, github: "mee6/citadel"}]
end

Modules

Citadel.Registry

>> Citadel.start()
:ok
>> Citadel.Registry.register("dumb_iex_process", self())
:ok
>> Citadel.Registry.find_by_key("dumb_iex_process")
#PID<0.80.0>
>> Citadel.Groups.join("dumb_group", self())
:ok
>> Citadel.Groups.members("dumb_group")
[#PID<0.80.0>]

When a process dies, it'll automatically be removed from the registry and the groups it used to belong to.

Citadel.Supervisor

This is a really simple distributed supervisor. Here's an example of how you can use it.

defmodule Worker do
    use GenServer

    def start_link(state) do
        GenServer.start_link(__MODULE__, state)
    end

    def init(state) do
        {:ok, state}
    end
    ...
end

defmodule Worker.Supervisor do
    def start_link do
        Citadel.Supervisor.start_link(__MODULE__)
    end

    def start_worker(worker_id) do
        Citadel.Supervisor.start_child(__MODULE__, Worker, ["kek"], id: worker_id)
    end

    def worker_lookup(worker_id) do
        Citadel.Supervisor.lookup(__MODULE__, worker_id)
    end

    def members do
        Citadel.Supervisor.members(__MODULE__)
    end
end

We then start a node iex --name [email protected] -S mix.

>> Citadel.start()
:ok
>> Worker.Supervisor.start_link()
{:ok, #PID<0.82.0>}
>> # Now we start a worker
nil
>> Worker.Supervisor.start_worker(0)
#PID<0.32.0>

Let's now connect a new node to the cluster. iex --name [email protected] -S mix.

>> Node.connect(:"[email protected]")
:ok
>> Citadel.start()
:ok
>> Worker.Supervisor.start_link()
{:ok, #PID<0.32.0>}
>> # Now if we start a worker it'll either be started here or on the n1 node. Depending on the hash of its id
nil
>> Worker.Supervisor.start_worker(1337)
#PID<1.43.0>

Citadel.Nodes (redis backed node discovery)

If you want to enable that feature you should start your application with CITADEL_REDIS_URL and CITADEL_DOMAIN env variables. The CITADEL_DOMAIN is basically the name of the "cluster" you want your node to be in.

>> Citadel.Nodes.init()
:ok
>> Citadel.members()
[:"[email protected]", :"[email protected]"]
>> Citadel.join_cluster()
[true, true]