docker_command.sh

#!/usr/bin/env bash

mix ecto.migrate
exec mix phoenix.server

docker_compose.yml

version: '2'

services:
# the database image
  db:
    image: "postgres:9.6"
    ports:
      - "5432:5432"
    environment:
      POSTGRES_USER: "gottserver"
      POSTGRES_PASSWORD: "asdf"
      POSTGRES_DB: "gottserver_prod"
    volumes:
      - data:/var/lib/postgresql/data

  # the main image, this is the application
  web:
    build: "."
    environment:
      MIX_ENV: "prod"
      PORT: "80"
      DB_USER: "gottserver"
      DB_PASSWORD: "asdf"
    ports:
      - "80:80"
    links:
      - "db:db"

# for persistence of database data
volumes:
  data:
    external: true

dockerfile

FROM ubuntu:16.04

RUN locale-gen en_US.UTF-8
RUN locale-gen de_CH.UTF-8
ENV LANG en_US.UTF-8
ENV LANGUAGE en_US:en
ENV LC_ALL de_CH.UTF-8

RUN apt-get update && apt-get install -y -q apt-transport-https wget build-essential # build -ssential includes make

# installing elixir
RUN wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb && dpkg -i erlang-solutions_1.0_all.deb
RUN apt-get update && apt-get install -y --no-install-recommends esl-erlang elixir

# gottserver specific
ADD . /app
WORKDIR /app

RUN mix local.hex --force
RUN mix local.rebar --force
RUN mix deps.get --only-prod
RUN MIX_ENV=prod mix compile
CMD ./docker_cmd.sh

usage

chmod +x docker_command.sh # one time deal
docker volume create --name=data # one time deal

docker-compose up -d --build