Elixir docker deployment

Dockerfile

ARG OTP_VERSION=22.0

##################################################
# Base - setup project and docker cache for build
FROM erlang:${OTP_VERSION}-alpine as base

# elixir expects utf8.
ENV ELIXIR_VERSION="v1.9.1" \
	LANG=C.UTF-8

RUN set -xe \
	&& ELIXIR_DOWNLOAD_URL="https://github.com/elixir-lang/elixir/archive/${ELIXIR_VERSION}.tar.gz" \
	&& ELIXIR_DOWNLOAD_SHA256="94daa716abbd4493405fb2032514195077ac7bc73dc2999922f13c7d8ea58777" \
	&& buildDeps=' \
		ca-certificates \
		curl \
		make \
	' \
	&& apk add --no-cache --virtual .build-deps $buildDeps \
	&& curl -fSL -o elixir-src.tar.gz $ELIXIR_DOWNLOAD_URL \
	&& echo "$ELIXIR_DOWNLOAD_SHA256  elixir-src.tar.gz" | sha256sum -c - \
	&& mkdir -p /usr/local/src/elixir \
	&& tar -xzC /usr/local/src/elixir --strip-components=1 -f elixir-src.tar.gz \
	&& rm elixir-src.tar.gz \
	&& cd /usr/local/src/elixir \
	&& make install clean \
	&& apk del .build-deps
  
# Install building packages
RUN apk --no-cache add git
RUN mix do local.hex --force, local.rebar --force

WORKDIR /build

# Cache dependencies
COPY ./mix.* ./
RUN mix deps.get

# Cache configs
COPY ./config ./config

#################################################
# Builder - stage for running lint, test and dev
FROM base as builder

WORKDIR /build
COPY . .
RUN rm -rf ./_build

##########################################
# Release - builds release for production
FROM builder as release

ENV MIX_ENV prod

WORKDIR /build

RUN mix do phx.digest, release

#######################################
# Script runner - minimal script runner environment
FROM alpine:3.9 as runner

RUN apk add --update --no-cache bash openssl curl

WORKDIR /app

COPY --from=release /build/_build/prod/rel/myapp ./
RUN chown -R nobody: /app
USER nobody

#######################################
# Runtime - minimal production runtime
FROM runner as runtime

# Set APP_VERSION at last, to reuse cached layers
ARG APP_VERSION
ENV APP_VERSION $APP_VERSION

ENV PORT 4040
EXPOSE $PORT

# Set release binary as entrypoint, no shell access
ENTRYPOINT ["/app/bin/myapp"]
CMD ["myapp"]

heroku.yml

setup:
  addons:
    - plan: heroku-postgresql
  config:
    PORT: 80
build:
  docker:
    web: Dockerfile
    release:
       dockerfile: Dockerfile
       target: runner
release:
  image: release
  command:
   - /app/bin/myapp eval 'MyApp.ReleaseTasks.migrate()'

release_tasks.ex

defmodule MyApp.ReleaseTasks do
  require Logger

  @repo_apps [
    :crypto,
    :ssl,
    :postgrex,
    :ecto_sql
  ]
  @repos Application.get_env(:my_app, :ecto_repos, [])

  def migrate(args \\ []) do
    {:ok, _} = Application.ensure_all_started(:logger)
    Logger.info("[task] running migrate")
    start_repo()

    run_migrations(args)

    Logger.info("[task] finished migrate")
    stop()
  end

  defp start_repo() do
    IO.puts("Starting dependencies...")

    Enum.each(@repo_apps, fn app ->
      {:ok, _} = Application.ensure_all_started(app)
    end)

    IO.puts("Starting repos...")
    :ok = Application.load(:my_app)

    Enum.each(@repos, fn repo ->
      {:ok, _} = repo.start_link(pool_size: 2)
    end)
  end

  defp run_migrations(args) do
    Enum.each(@repos, fn repo ->
      app = Keyword.get(repo.config(), :otp_app)
      IO.puts("Running migrations for #{app}")

      case args do
        ["--step", n] -> migrate(repo, :up, step: String.to_integer(n))
        ["-n", n] -> migrate(repo, :up, step: String.to_integer(n))
        ["--to", to] -> migrate(repo, :up, to: to)
        ["--all"] -> migrate(repo, :up, all: true)
        [] -> migrate(repo, :up, all: true)
      end
    end)
  end

  defp migrate(repo, direction, opts) do
    migrations_path = priv_path_for(repo, "migrations")
    Ecto.Migrator.run(repo, migrations_path, direction, opts)
  end

  defp priv_path_for(repo, filename) do
    app = Keyword.get(repo.config(), :otp_app)
    priv_dir = Application.app_dir(app, "priv")

    Path.join([priv_dir, "repo", filename])
  end

  defp stop() do
    IO.puts("Stopping...")
    :init.stop()
  end
end