docker-compose.yml

version: "3.4"

services:
  app:
    build:
      context: "."
      target: app
      args:
        ENV: dev
    environment:
      DATABASE_URL: "psql://postgres:postgres@db/app"
    ports:
      - "4000:4000"
    volumes:
      - "app:/app"
    command: mix do deps.get, ecto.migrate, phx.server

  assets:
    build:
      context: "."
      target: assets
    command: sh -c "npm install && npm run watch"
    volumes:
      - "app:/app"

  db:
    image: postgres:10
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_DB: app

  sync:
    image: cweagans/bg-sync
    volumes:
      - ".:/source"
      - "app:/destination"

    environment:
      SYNC_EXTRA_UNISON_PROFILE_OPTS: |
        ignore = Path assets/node_modules/*
        ignore = Path _build/*

volumes:
  app:

Dockerfile

FROM node:12.2-slim as assets

WORKDIR /app/assets

COPY assets/package*.json ./

RUN npm install

# Copy the entire app so we can put files into /app/priv/static
COPY . /app

RUN npm run deploy

FROM elixir:1.8.1-slim as app

RUN apt-get update && \
  apt-get install -y inotify-tools && \
  rm -rf /var/lib/apt/lists/*

WORKDIR /app

RUN mix local.hex --force
RUN mix local.rebar --force

ARG ENV=dev
ENV ENV $ENV

COPY mix.* ./

RUN mix deps.get
RUN mix deps.compile

COPY . .

RUN mix compile

COPY --from=assets /app/priv/static/* /app/priv/static/

RUN mix phx.digest

CMD mix phx.server

# TODO: Add packaging once elixir 1.9 is released