Docker container cannot access postgres

Hello.
I’m trying to make a container of database server which is in phoenix.

Dockerfile

FROM erlang:23

# elixir expects utf8.
ENV ELIXIR_VERSION="v1.10.4" \
	LANG=C.UTF-8

RUN set -xe \
	&& ELIXIR_DOWNLOAD_URL="https://github.com/elixir-lang/elixir/archive/${ELIXIR_VERSION}.tar.gz" \
	&& ELIXIR_DOWNLOAD_SHA256="8518c78f43fe36315dbe0d623823c2c1b7a025c114f3f4adbb48e04ef63f1d9f" \
	&& curl -fSL -o elixir-src.tar.gz $ELIXIR_DOWNLOAD_URL \
	&& echo "$ELIXIR_DOWNLOAD_SHA256  elixir-src.tar.gz" | sha256sum -c - \
	&& mkdir -p /usr/local/src/elixir \
	&& tar -xzC /usr/local/src/elixir --strip-components=1 -f elixir-src.tar.gz \
	&& rm elixir-src.tar.gz \
	&& cd /usr/local/src/elixir \
	&& make install clean

WORKDIR /app

RUN apt-get -y update &&\
    mix local.hex --force && \
    mix archive.install hex phx_new --force

docker-compose.yml

version: '3'

services:
  PostgreSQL:
    image: postgres
    container_name: postgres
    ports:
      - 5432:5432
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_INITDB_ARGS: "--encoding=UTF-8"
    hostname: localhost
    restart: always
    user: root
  elixir:
    build: .
    ports:
      - 4040:4000
    container_name: elixir
    volumes:
      - .:/app
    depends_on:
      - PostgreSQL
    command: /bin/bash
    tty: true
    stdin_open: true

In my Dockerfile, I can not use elixir:10.4 image directly due to erlang version. I copied the content of Dockerfile from docker-elixir.

I can run phoenix server without ecto, but cannot run with ecto… When the server access to postgres, it shows errors.

[error] `inotify-tools` is needed to run `file_system` for your system, check https://github.com/rvoicilas/inotify-tools/wiki for more information about how to install it. If it's already installed but not be found, appoint executable file with `config.exs` or `FILESYSTEM_FSINOTIFY_EXECUTABLE_FILE` env.
[warn] Could not start Phoenix live-reload because we cannot listen to the file system.
You don't need to worry! This is an optional feature used during development to
refresh your browser when you save files and it does not affect production.

[error] Postgrex.Protocol (#PID<0.383.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.389.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.386.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.380.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.388.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.382.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.385.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.381.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.387.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.384.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[info] Running MilkWeb.Endpoint with cowboy 2.8.0 at 0.0.0.0:4000 (http)
[info] Access MilkWeb.Endpoint at http://localhost:4000
[error] Postgrex.Protocol (#PID<0.386.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.383.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.380.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.389.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.388.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.381.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.385.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.384.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.382.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.387.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused

I’ve checked database config in my dev.exs.

use Mix.Config

# Configure your database
config :milk, Milk.Repo,
  username: "postgres",
  password: "postgres",
  database: "milk_dev",
  hostname: "localhost",
  show_sensitive_data_on_connection_error: true,
  pool_size: 10

I entered these command in the phoenix root directory.(The Dockerfile and docker-compose.yml exist there)

> docker-compose up -d --build                                                                                15:32
Building elixir
Step 1/5 : FROM erlang:23
 ---> d827a7cccc2f
Step 2/5 : ENV ELIXIR_VERSION="v1.10.4" 	LANG=C.UTF-8
 ---> Using cache
 ---> 12333fd4f990
Step 3/5 : RUN set -xe 	&& ELIXIR_DOWNLOAD_URL="https://github.com/elixir-lang/elixir/archive/${ELIXIR_VERSION}.tar.gz" 	&& ELIXIR_DOWNLOAD_SHA256="8518c78f43fe36315dbe0d623823c2c1b7a025c114f3f4adbb48e04ef63f1d9f" 	&& curl -fSL -o elixir-src.tar.gz $ELIXIR_DOWNLOAD_URL 	&& echo "$ELIXIR_DOWNLOAD_SHA256  elixir-src.tar.gz" | sha256sum -c - 	&& mkdir -p /usr/local/src/elixir 	&& tar -xzC /usr/local/src/elixir --strip-components=1 -f elixir-src.tar.gz 	&& rm elixir-src.tar.gz 	&& cd /usr/local/src/elixir 	&& make install clean
 ---> Using cache
 ---> adde3f1e08c1
Step 4/5 : WORKDIR /app
 ---> Using cache
 ---> 9465f23940f9
Step 5/5 : RUN apt-get -y update &&    mix local.hex --force &&     mix archive.install hex phx_new --force
 ---> Using cache
 ---> d44a916ff543

Successfully built d44a916ff543
Successfully tagged milk_elixir:latest
postgres is up-to-date
elixir is up-to-date

> docker ps -a                                                                                                15:36
CONTAINER ID        IMAGE                         COMMAND                  CREATED             STATUS                      PORTS                    NAMES
ce17c652d127        postgres                      "docker-entrypoint.s…"   25 minutes ago      Up 25 minutes               0.0.0.0:5432->5432/tcp   postgres
3bc705d314fc        milk_elixir                   "/bin/bash"              34 minutes ago      Up 34 minutes               0.0.0.0:4040->4000/tcp   elixir

> docker exec -it elixir bash                                                                                 15:36
root@3bc705d314fc:/app# mix phx.server
[error] `inotify-tools` is needed to run `file_system` for your system, check https://github.com/rvoicilas/inotify-tools/wiki for more information about how to install it. If it's already installed but not be found, appoint executable file with `config.exs` or `FILESYSTEM_FSINOTIFY_EXECUTABLE_FILE` env.
[warn] Could not start Phoenix live-reload because we cannot listen to the file system.
You don't need to worry! This is an optional feature used during development to
refresh your browser when you save files and it does not affect production.

[error] Postgrex.Protocol (#PID<0.388.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.385.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.387.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.381.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.383.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.386.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.384.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.389.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.382.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[error] Postgrex.Protocol (#PID<0.380.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
[info] Running MilkWeb.Endpoint with cowboy 2.8.0 at 0.0.0.0:4000 (http)
[info] Access MilkWeb.Endpoint at http://localhost:4000
^C

I don’t know where the setting is incorrect.
I can show any information about the project. Help me!