Docker Compose setup for Elixir, Phoenix, and Postgres

dev.exs

# config/dev.exs

config :yourapp, YourApp.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"),

  ...

docker-compose.yml

version: '3.8'
services:
  web:
    build: .
    ports:
      - "4000:4000"
    volumes:
      - .:/app
    depends_on:
      - db
    env_file:
      - some_app.env

  db:
    image: postgres:latest
    environment:
      - POSTGRES_USER=some_user
      - POSTGRES_PASSWORD=some_password
    volumes:
      - ./postgres-data:/var/lib/postgresql/data
    ports:
      - "5432:5432"

Dockerfile

FROM elixir:latest

# Install debian packages
RUN apt-get update && \
    apt-get install --yes build-essential inotify-tools postgresql-client git && \
    apt-get clean

ADD . /app

# Install Phoenix packages
RUN mix local.hex --force && \
    mix local.rebar --force && \
    mix archive.install --force hex phx_new 1.5.1

# Install node
RUN curl -sL https://deb.nodesource.com/setup_14.x | bash - && apt-get install -y nodejs

WORKDIR /app

RUN mix deps.get
RUN npm install --prefix ./assets

EXPOSE 4000

CMD ["/app/entrypoint.sh"]

entrypoint.sh

#!/bin/bash
# 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

some_app.env

PGUSER=some_user
PGPASSWORD=some_password
PGDATABASE=some_database
PGPORT=5432
PGHOST=db

Could you share me what is expected folder structure? I was doing little near but always stuck at RUN mix deps.get due to Could not find a Mix.Project error.