Bootloader

Bootloader provides full control over the application lifecycle in Elixir.

Usage

Bootloader acts as a shim to the initialization sequence for your application's VM. Using Bootloader, you can ensure that the VM will always pass initialization. This provides the running target the ability of using Elixir / Erlang to control the full application lifecycle through the exposure of new system phases.

Heres how it works. Include bootloader into your application release plugins.

# rel/config.exs

release :simple_app do
  set version: current_version(:simple_app)
  plugin Bootloader
end

And produce a release

$ mix release

Go to the release directory and boot your app using bootloader

$ _build/dev/rel/simple_app/bin/simple_app console_boot bootloader

From here we can see that the bootloader was started, but simple_app was not.

iex(simple_app@127.0.0.1)1> Application.started_applications
[{:iex, &#39;iex&#39;, &#39;1.4.0&#39;}, {:bootloader, &#39;bootloader&#39;, &#39;0.1.0&#39;},
 {:elixir, &#39;elixir&#39;, &#39;1.4.0&#39;}, {:compiler, &#39;ERTS  CXC 138 10&#39;, &#39;7.0.3&#39;},
 {:stdlib, &#39;ERTS  CXC 138 10&#39;, &#39;3.2&#39;}, {:kernel, &#39;ERTS  CXC 138 10&#39;, &#39;5.1.1&#39;}]

Now lets configure bootloader to do something more interesting by adding some general configuration.

Lets have it start our application and initialize some apps before our app starts

# config/config.exs

config :bootloader,
  overlay_path: "/tmp/erl_bootloader",
  init: [:runtime_app],
  app: :simple_app