Mix release -- deployment tasks

I have a Phoenix application that uses elasticsearch-elixir. I’m deploying with Mix releases, and trying to call an indexing function against this compiled release.

The docs have a guide on running these tasks in a Distillery release. They suggest adding the following module:

defmodule Backend.Release do
  # OTP apps that must be started in order for the code in this module
  # to function properly.
  #
  # Don't forget about Ecto and Postgrex if you're using Ecto to load documents
  # in your Elasticsearch.Store module!
  @start_apps [
    :crypto,
    :ssl,
    :postgrex,
    :ecto,
    :elasticsearch
  ]

  # Ecto repos to start, if any
  @repos Application.get_env(:my_app, :ecto_repos, [])

  # Elasticsearch clusters to start
  @clusters [Backend.Elasticsearch.Cluster]

  # Elasticsearch indexes to build
  @indexes [:instances]

  def build_elasticsearch_indexes() do
    start_services()
    IO.puts("Building indexes...")
    Enum.each(@indexes, &Elasticsearch.Index.hot_swap(Backend.Elasticsearch.Cluster, &1))
    stop_services()
  end

  # Ensure that all OTP apps, repos used by your Elasticsearch store,
  # and your Elasticsearch Cluster(s) are started
  defp start_services do
    IO.puts("Starting dependencies...")
    Enum.each(@start_apps, &Application.ensure_all_started/1)

    IO.puts("Starting repos...")
    Enum.each(@repos, & &1.start_link(pool_size: 1))

    IO.puts("Starting clusters...")
    Enum.each(@clusters, & &1.start_link())
  end

  defp stop_services do
    :init.stop()
  end
end

I’ve tried this setup, and then running my_app eval "MyApp.ReleaseTasks.build_elasticsearch_indexes" against the compiled binary. However, it causes an error:

Starting dependencies...
Starting repos...
Starting clusters...
Building indexes...
** (exit) exited in: GenServer.call(Backend.Elasticsearch.Cluster, :config, 5000)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
    (elixir) lib/gen_server.ex:1000: GenServer.call/3
    (elasticsearch) lib/elasticsearch/indexing/index.ex:32: Elasticsearch.Index.hot_swap/2
    (elixir) lib/enum.ex:783: Enum."-each/2-lists^foreach/1-0-"/2
    (elixir) lib/enum.ex:783: Enum.each/2
    lib/backend/release.ex:29: Backend.Release.build_elasticsearch_indexes/0
    (stdlib) erl_eval.erl:680: :erl_eval.do_apply/6
    (elixir) lib/code.ex:240: Code.eval_string/3

I think I remember reading somewhere that Application.ensure_all_started is no longer the recommended way to do something like this, but I can’t find it now. Does the above module look reasonable for Elixir 1.9 releases? Is there an obvious reason I’m missing that this doesn’t work?