This library is a strategy for libcluster for connecting nodes in Google App Engine. If you're unfamiliar with libcluster, please read the documentation.

This library makes the assumption that the elixir application is using Distillery releases.

Installation

Add :libcluster_gae to your project's mix dependencies.

def deps do
  [
    {:libcluster_gae, "~> 0.1"}
  ]
end

Deployment Assumptions

Clustering will only apply to nodes that are configured to receive HTTP traffic in App Engine are currently running and belong to the same service. If this doesn't fit your deployment strategy, please open a Github issue describing your deployment configuration.

Configuration

Google Cloud

Before clustering can work, enable the App Engine Admin API for your application's Google Cloud Project. Follow the guide on enabling APIs.

Elixir Application

To cluster an application running in Google App Engine, define a topology for libcluster.

# config.exs
config :libcluster,
  topologies: [
    my_app: [
      strategy: Cluster.Strategy.GoogleAppEngine
    ]
  ]

Make sure a cluster supervisor is part of your application.

defmodule MyApp.App do
  use Application

  def start(_type, _args) do
    topologies = Application.get_env(:libcluster, :topologies)

    children = [
      {Cluster.Supervisor, [topologies, [name: MyApp.ClusterSupervisor]]},
      # ...
    ]
    Supervisor.start_link(children, strategy: :one_for_one, name: MyApp.Supervisor)
  end
end

Update your release's vm.args file to include the following lines.

## Name of the node
-name <%= release_name%>@${GAE_INSTANCE}.c.${GOOGLE_CLOUD_PROJECT}.internal

## Limit distributed erlang ports to a single port
-kernel inet_dist_listen_min 9999
-kernel inet_dist_listen_max 9999

Update the app.yaml configuration file for Google App Engine.

env_variables:
  REPLACE_OS_VARS: true

network:
  forwarded_ports:
    # epmd
    - 4369
    # erlang distribution
    - 9999

Now run gcloud app deploy and enjoy clustering on GAE!