Phoenix with docker compose

.env

PGHOST=db
PGUSER=postgres
PGPASSWORD=postgres
PGDATABASE=hello_dev
PGPORT=5432

dev.exs

config :hello, Hello.Repo,
  username: System.get_env("PGUSER"),
  password: System.get_env("PGPASSWORD"),
  database: System.get_env("PGDATABASE"),
  hostname: System.get_env("PGHOST"),
  port:     System.get_env("PGPORT"),
  ...
  
config :hello, HelloWeb.Endpoint,
  http: [ip: {0, 0, 0, 0}, port: 4000],

docker-compose.yml

version: '3.9'

services:
  db:
    image: postgres:14.4-alpine
    volumes:
      - pgdata:/var/lib/postgresql/data
    environment:
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=postgres

  app:
    build: .
    environment:
      - MIX_ENV=dev
    env_file:
      - .env
    depends_on:
      - db
    ports:
      - 4000:4000
    volumes:
      - .:/app

volumes:
  pgdata:

Dockerfile

FROM elixir:1.14-alpine

# install debian packages
RUN apk add --no-cache &&\
  apk add --virtual build-dependencies\
  build-base\
  inotify-tools\
  postgresql-client\
  vim\
  git


WORKDIR /app
COPY mix.exs .
COPY mix.lock .
ADD . /app

# install phoenix packages
RUN mix local.hex --force && \
  mix local.rebar --force && \ 
  mix archive.install --force hex phx_new

RUN mix deps.get


EXPOSE 4000
CMD ["/app/entrypoint.sh"]

entrypoint.sh

#!/bin/sh
# Docker entrypoint script.

# Wait until Postgres is ready
echo "Testing if Postgres is accepting connections. {$PGHOST} {$PGPORT} ${PGUSER}"
while ! pg_isready -q -h $PGHOST -p $PGPORT -U $PGUSER
do
  echo "$(date) - waiting for database to start"
  sleep 2
done

# Create, migrate, and seed database if it doesn't exist.
if [[ -z `psql -Atqc "\\list $PGDATABASE"` ]]; then
  echo "Database $PGDATABASE does not exist. Creating..."
  mix ecto.create
  mix ecto.migrate
  mix run priv/repo/seeds.exs
  echo "Database $PGDATABASE created."
fi

exec mix phx.server

instructions

Head over to (installation)['https://hexdocs.pm/phoenix/installation.html') if you don't have elixir, hex or phoenix application generator installed

1. Run the phoenix generator with your app name
  $ mix phx.new hello

if prompted on cli to install app dependencies type Y

2. Copy the above files to the application you just generated.
3. make the entrypoint.sh an executable
   $ sudo chmod a+x entrypoint.sh