Singleton

Convenience wrapper library around Erlang's global module to ensure a single instance of a process is kept running on a cluster of nodes.

Installation

The package can be installed as:

1. Add singleton to your list of dependencies in mix.exs:

```elixir
def deps do
  [{:singleton, "~> 1.0.0"}]
end
```

2. Ensure singleton is started before your application:

```elixir
def application do
  [applications: [:singleton]]
end
```

Usage

Use Singleton.start_child/3 to start a unique GenServer process.

Singleton.start_child(MyServer, [1], {:myserver, 1})

Execute this command on all nodes. The MyServer GenServer is now globally registered under the name {:global, {:myserver, 1}}.

As soon as you connect nodes together, you'll see logger messages like:

04:56:29.003 [info]  global: Name conflict terminating {MyServer, #PID<12501.68.0>}

When you now stop (or disconnect) the node on which the singleton process runs, you'll see it get started on one of the other nodes.

Troubleshooting

More than 3 singleton processes [info] Application singleton exited: shutdown

In case you run more than 3 singleton you'll need to increase the max_restarts of DynamicSupervisor.

config :singleton,
  dynamic_supervisor: [max_restarts: 100]