我正在尝试将现有项目移动到Docker。我在M.Academy上遵循了本教程，并在现有项目上遵循了Docker的设置说明
当执行尝试连接MySQL时，我收到此错误ERROR 2002（HY 000）：无法连接到“db”上的MySQL服务器（115）
我还试图执行：telnet db 3306
响应：正在尝试172.17.0.1...远程登录：无法连接到远程主机：联机逾时
我尝试了所有的方法，但还是不能解决问题。我是Docker的新手。我使用的是Ubuntu 18.04 LTE。在导入数据库之前，没有更改db.env，并且在其他任何步骤上都没有错误。
我进一步检查，发现容器无法与MySQL建立连接。
P.S.我能够通过使用（外部MySQL端口）mysql -h 127.0.01 -u root -p -P 3306成功连接Docker容器外部的相同MySQL服务

重现步骤

1.在Ubuntu 18.04上安装Docker和Docker Compose
1.下载Docker合成模板：curl -s https://raw.githubusercontent.com/markshust/docker-magento/master/lib/template | bash
1.替换为现有Magento示例的现有源代码：cp -R ~/Sites/existing src
1.执行：docker-compose -f docker-compose.yml up -d
1.将文件复制到容器：bin/copytocontainer --all
1.导入现有数据库：bin/mysql < /var/www/magento243.sql

预期结果数据库应已成功导入
实际结果错误2002（HY 000）：无法连接到'db'上的MySQL服务器（115）

P.S.问题已在此处提出：https://github.com/markshust/docker-magento/issues/589

停靠-撰写.yml

version: "3"

services:
  app:
    image: markoshust/magento-nginx:1.18-5
    ports:
      - "80:8000"
      - "443:8443"
    depends_on:
      - "db"
    volumes: &appvolumes
      - ~/.composer:/var/www/.composer:cached
      - ~/.ssh/id_rsa:/var/www/.ssh/id_rsa:cached
      - ~/.ssh/known_hosts:/var/www/.ssh/known_hosts:cached
      - appdata:/var/www/html
      - sockdata:/sock
      - ssldata:/etc/nginx/certs
    extra_hosts: &appextrahosts
      ## M1 Mac support to fix Docker delay, see #566
      - "app:172.17.0.1"
      - "phpfpm:172.17.0.1"
      - "db:172.17.0.1"
      - "redis:172.17.0.1"
      - "elasticsearch:172.17.0.1"
      - "rabbitmq:172.17.0.1"
      ## Selenium support, replace "magento.test" with URL of your site
      - "magento.test:172.17.0.1"

  phpfpm:
    image: markoshust/magento-php:7.4-fpm-11
    volumes: *appvolumes
    extra_hosts: *appextrahosts
    env_file: env/phpfpm.env

  db:
    image: mariadb:10.4
    command: --max_allowed_packet=256M
    ports:
      - "3306:3306"
    env_file: env/db.env
    volumes:
      - dbdata:/var/lib/mysql
    extra_hosts: *appextrahosts

  redis:
    image: redis:5.0-alpine
    ports:
      - "6379:6379"
    extra_hosts: *appextrahosts

  elasticsearch:
    image: markoshust/magento-elasticsearch:7.9.3-1
    ports:
      - "9200:9200"
      - "9300:9300"
    environment:
      - "discovery.type=single-node"
      ## Set custom heap size to avoid memory errors
      - "ES_JAVA_OPTS=-Xms1g -Xmx1g"
      ## Avoid test failures due to small disks
      ## More info at https://github.com/markshust/docker-magento/issues/488
      - "cluster.routing.allocation.disk.threshold_enabled=false"
      - "index.blocks.read_only_allow_delete"
    extra_hosts: *appextrahosts

  rabbitmq:
    image: rabbitmq:3.8.22-management-alpine
    ports:
      - "15672:15672"
      - "5672:5672"
    volumes:
      - rabbitmqdata:/var/lib/rabbitmq
    environment:
      - RABBITMQ_VM_MEMORY_HIGH_WATERMARK=1GB
    extra_hosts: *appextrahosts

  mailcatcher:
    image: sj26/mailcatcher
    ports:
      - "1080:1080"
    extra_hosts: *appextrahosts

  ## Selenium support, uncomment to enable
  #selenium:
  #  image: selenium/standalone-chrome-debug:3.8.1
  #  ports:
  #    - "5900:5900"
  #  extra_hosts: *appextrahosts

volumes:
  appdata:
  dbdata:
  rabbitmqdata:
  sockdata:
  ssldata: