Can't run Phoenix using docker-compose

Hi, I am trying to get Phoenix app work using containers and elixir releases.

I succeeded to run my app in a single container and connect it to local postgres using dockerfile and command below:

Dockerfile:

FROM elixir:1.9.0-alpine AS build

# install build dependencies
RUN apk add --no-cache build-base npm git python

# prepare build dir
WORKDIR /app

# install hex + rebar
RUN mix local.hex --force && \
    mix local.rebar --force

# set build ENV
ENV MIX_ENV=prod

# install mix dependencies
COPY mix.exs mix.lock ./
COPY config config
RUN mix do deps.get, deps.compile

# build assets
COPY assets/package.json assets/package-lock.json ./assets/
RUN npm --prefix ./assets ci --progress=false --no-audit --loglevel=error

COPY priv priv
COPY assets assets
RUN npm run --prefix ./assets deploy
RUN mix phx.digest

# compile and build release
COPY lib lib
# uncomment COPY if rel/ exists
# COPY rel rel
RUN mix do compile, release

# prepare release image
FROM alpine:3.9 AS app
RUN apk add --no-cache openssl ncurses-libs

EXPOSE 4000
ENV PORT=4000 \
    MIX_ENV=prod \
    SHELL=/bin/bash

WORKDIR /app

RUN chown nobody:nobody /app

USER nobody:nobody

COPY --from=build --chown=nobody:nobody /app/_build/prod/rel/myapp ./

ENV HOME=/app

CMD ["bin/myapp", "start"]

Commands:

docker build -t test .

docker run \
  --network=host \
  -e DATABASE_URL=postgresql://postgres:postgres@localhost/myapp_dev \
  -e SECRET_KEY_BASE=...some key... \
  -e HOST=localhost \
  test    

But when I am trying to up two containers via docker-compose.yml

version: '3'

services:
  PostgreSQL:
    image: postgres
    container_name: postgres
    ports:
      - 5433:5432
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_INITDB_ARGS: "--encoding=UTF-8"
    hostname: postgres
    restart: always
    user: root
  elixir:
    build:
      context: .
      dockerfile: Dockerfile
    env_file:
      - .env.list
    ports:
      - 4040:4000
    container_name: elixir
    volumes:
      - .:/app
    depends_on:
      - PostgreSQL

.env.list:

DATABASE_URL=postgresql://postgres:postgres@postgres/myapp_prod
SECRET_KEY_BASE=... some key...
HOST=localhost

I am getting an error:

Creating postgres ... done
Creating elixir   ... error

ERROR: for elixir  Cannot start service elixir: OCI runtime create failed: container_linux.go:367: starting container process caused: exec: "bin/myapp": stat bin/myapp: no such file or directory: unknown
ERROR: Encountered errors while bringing up the project.

I suppose that docker-compose should just run elixir container with according dockerfile as just it happens with “docker run …”, but it seems that I get different container which doesn’t have bin/ directory for some reason. Am I missing something?