Libcluster Hop Strategy

Easily setup distributed Elixir on Hop!

This package so far contains one strategy, ClusterHop.Strategy.Deployment, which uses the Hop API to find all containers running under one deployment.
It will then attempt to register each container via the container internal IPs to each node.

Installation

0. Add Libcluster Hop as a dependency

Currently, this isn't available on Hex.pm, but in the meantime you can get it straight from GitHub like so:

defp deps do
    [
      # ... your other deps
      {:libcluster, "~> 3.3"},
      {:libcluster_hop,
       github: "hiett/libcluster_hop", ref: "6e3a00d2e8e8ea0388135d8c000b999536021909"} # (this is current stable ref)
    ]
end

1. Create a Hop Project Token

Create a project token with manage deployments permissions.

This token is used to get all the containers in a deployment from the Hop API.

2. Setup the strategy in your Application file

Here's an example of what a barebones Application file would look like:

defmodule HopTestapp do
  use Application

  def start(_type, _args) do
    IO.puts("Starting test app")

    topologies = [
      hop: [
        strategy: ClusterHop.Strategy.Deployment,
        config: [
          hop_token: "ptk_xxx",
          app_prefix: "my_amazing_app" # Optional, defaults to "app"
        ]
      ]
    ]

    children = [
      {Cluster.Supervisor, [topologies, [name: HopTestapp.ClusterSupervisor]]}
    ]

    opts = [strategy: :one_for_one, name: HopTestapp.Supervisor]

    Supervisor.start_link(children, opts)
  end
end

Fill in the hop_token and optionally app_prefix. Libcluster Hop will automatically find the internal container IP (starts with 10.1.x.x), and form a nodename in the following format: app_prefix@internal_ip

3. [Important!] Set the following Environment Variable in your Hop deployment:

RELEASE_DISTRIBUTION=none

You need to set this because Elixir will automatically attempt to start the application in distributed mode upon creation of a release. However, this will have the incorrect nodename, because internal IPs aren't instantly available to containers on Hop.

Libcluster Hop will start the node itself when it has obtained the IP and formed a nodename.

4. Scale away!

You're all good to go. All containers inside a deployment will now be linked together.