如何在docker-compose中将两个正在运行的容器彼此连接？

因此，我有一个简单的Python Flask应用程序，其中有2个服务：应用程序和数据库。我希望应用程序（Flask应用程序）连接到数据库服务（PostgreSQL）。

现在，当我注释掉Application服务并运行时docker-compose up，它将启动端口5432上公开的Database服务。然后当我在本地运行Flask应用并尝试连接时，它可以工作。

现在，我取消注释应用程序服务并运行docker-compose up --build。它构建并启动这两个服务。但是当我访问http：// localhost：5000时，由于连接错误（拒绝），应用程序崩溃了。

docker-compose.yml

version: '3.7'
services:
  application:
    depends_on:
      - database
    build: ./core
    restart: always
    networks:
      - cbr-open-data
    ports:
      - 5000:5000
    environment:
      FLASK_ENV: development
    volumes:
      - ./core:/app

  database:
    image: postgres
    restart: always
    networks:
      - cbr-open-data
    environment: 
      POSTGRES_USER:      ${DATABASE_USER}
      POSTGRES_PASSWORD:  ${DATABASE_PASSWORD}
      POSTGRES_DB:        ${DATABASE_NAME}
    ports:
      - 5432:5432
    volumes:
      - ./database:/var/lib/postgresql/data

networks:
  cbr-open-data:
    driver: bridge

config / connection.py

import psycopg2
import pandas

connection = psycopg2.connect(
    host = 'localhost',
    database = '...',
    user = '...',
    password = '...',
    port='5432'
)

users = pandas.read_sql('SELECT * FROM users', connection)

app.py

from flask import Flask, render_template
from config.connection import users

app = Flask(__name__)

@app.route('/')
def index():
    print(users)
    return render_template('index.html')

if __name__ == '__main__':
    app.run(debug=True)

错误

➜  cbr-open-data git:(master) ✗ docker-compose up
Creating network "cbr-open-data_cbr-open-data" with driver "bridge"
Creating cbr-open-data_database_1 ... done
Creating cbr-open-data_application_1 ... done
Attaching to cbr-open-data_database_1, cbr-open-data_application_1
application_1  |  * Environment: development
application_1  |  * Debug mode: on
application_1  |  * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
application_1  |  * Restarting with stat
application_1  |  * Debugger is active!
application_1  |  * Debugger PIN: 159-218-115
database_1     | 
database_1     | PostgreSQL Database directory appears to contain a database; Skipping initialization
database_1     | 
database_1     | 2020-02-09 18:10:37.188 UTC [1] LOG:  starting PostgreSQL 12.1 (Debian 12.1-1.pgdg100+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 8.3.0-6) 8.3.0, 64-bit
database_1     | 2020-02-09 18:10:37.189 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
database_1     | 2020-02-09 18:10:37.189 UTC [1] LOG:  listening on IPv6 address "::", port 5432
database_1     | 2020-02-09 18:10:37.192 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
database_1     | 2020-02-09 18:10:37.303 UTC [27] LOG:  database system was shut down at 2020-02-09 13:21:34 UTC
database_1     | 2020-02-09 18:10:37.330 UTC [1] LOG:  database system is ready to accept connections

THIS IS WHEN I VISIT THE FLASK APP ON 5000.

application_1  | 172.28.0.1 - - [09/Feb/2020 18:10:41] "GET / HTTP/1.1" 500 -
application_1  | Traceback (most recent call last):
application_1  |   File "/usr/local/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
application_1  |     raise value
application_1  |   File "/app/app.py", line 2, in <module>
application_1  |     from config.connection import users
application_1  |   File "/app/config/connection.py", line 9, in <module>
application_1  |     port='5432'
application_1  |   File "/usr/local/lib/python3.7/site-packages/psycopg2/__init__.py", line 126, in connect
application_1  |     conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
application_1  | psycopg2.OperationalError: could not connect to server: Connection refused
application_1  |        Is the server running on host "localhost" (127.0.0.1) and accepting
application_1  |        TCP/IP connections on port 5432?
application_1  | could not connect to server: Cannot assign requested address
application_1  |        Is the server running on host "localhost" (::1) and accepting
application_1  |        TCP/IP connections on port 5432?
application_1  | 172.28.0.1 - - [09/Feb/2020 18:10:41] "GET /?__debugger__=yes&cmd=resource&f=style.css HTTP/1.1" 200 -
application_1  | 172.28.0.1 - - [09/Feb/2020 18:10:41] "GET /?__debugger__=yes&cmd=resource&f=debugger.js HTTP/1.1" 200 -
application_1  | 172.28.0.1 - - [09/Feb/2020 18:10:41] "GET /?__debugger__=yes&cmd=resource&f=jquery.js HTTP/1.1" 200 -
application_1  | 172.28.0.1 - - [09/Feb/2020 18:10:42] "GET /?__debugger__=yes&cmd=resource&f=ubuntu.ttf HTTP/1.1" 200 -
application_1  | 172.28.0.1 - - [09/Feb/2020 18:10:42] "GET /?__debugger__=yes&cmd=resource&f=console.png HTTP/1.1" 200 -

有人可以解释为什么我在本地运行应用程序时数据库服务拒绝来自应用程序服务的连接但接受连接吗？我想对未来的实践有个更好的理解。

我已经尝试过的

• 将这两种服务都添加到了自己创建的网络（cbr-open-data）中。但是仍然没有解决方案。
• 看到这link是有可能的，但是docker不建议这样做，因为它可能会从将来的更新中删除。

非常感谢所有帮助！提前致谢。