Docker部署的PHP(Symfony)应用连接AWS RDS(MariaDB)失败

场景与配置 #

在EC2实例上通过Docker运行PHP（Symfony）应用，对应的Docker Compose配置如下：

version: "3.7"

services:
  traefik:
    image: traefik:1.7
    container_name: so-traefik
    command: --docker --docker.exposedbydefault=false
    ports:
      - "80:80"
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock

  app:
    image: thecodingmachine/php:7.2-v4-apache
    container_name: so-app
    labels:
      - traefik.enable=true
      - traefik.backend=app
      - traefik.frontend.rule=Host:so.localhost
    environment:
      APACHE_DOCUMENT_ROOT: web
      PHP_INI_MEMORY_LIMIT: 1G
      PHP_INI_ERROR_REPORTING: E_ALL
      PHP_INI_UPLOAD_MAX_FILESIZE: 512M
      PHP_INI_POST_MAX_SIZE: 512M
      PHP_INI_MAX_INPUT_VARS: 4096
      PHP_INI_MAX_EXECUTION_TIME: 500
      PHP_EXTENSION_GD: 1
      PHP_EXTENSION_IMAGICK: 1
      PHP_EXTENSION_INTL: 1
      PHP_EXTENSION_XDEBUG: 0
      PHP_EXTENSION_BCMATH: 1
      PHP_INI_XDEBUG__REMOTE_AUTOSTART: 0
      PHP_INI_XDEBUG__MAX_NESTING_LEVEL: 5000
      SYMFONY_ENV: prod
    working_dir: /var/www/html
    volumes:
      - "./website:/var/www/html"
      - "./website/vendor:/var/www/html/vendor:cached"

问题现象 #

可以通过Docker CLI执行mysql -h ${HOST} -P 3306 -u ${USER} -D ${DB} -p（其中HOST为AWS RDS端点）成功连接数据库，说明容器能正常解析主机名。但执行任何访问数据库的Symfony命令时，都会出现连接错误：

docker@724cef2e8b7a:/var/www/html$ php bin/console doctrine:query:sql 'SELECT * FROM product;'
11:27:30 ERROR     [console] Error thrown while running command "doctrine:query:sql 'SELECT * FROM product;'" Message: "An exception occured in driver: SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Name or service not known" ["exception" => Doctrine\DBAL\Exception\ConnectionException { …},"command" => "doctrine:query:sql 'SELECT * FROM product;'","message" => "An exception occured in driver: SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Name or service not known"]

In AbstractMySQLDriver.php line 103:
                                                                                                                                  
  An exception occured in driver: SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Name or service not known  
                                                                                                                                  

In PDOConnection.php line 47:
                                                                                                  
  SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Name or service not known  
                                                                                                 

In PDOConnection.php line 43:
                                                                                                  
  SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo failed: Name or service not known  
                                                                                                 

In PDOConnection.php line 43:
                                                                                               
  PDO::__construct(): php_network_getaddresses: getaddrinfo failed: Name or service not known

参数配置 #

parameters.dist文件已配置正确的数据库主机名及相关参数：

# This file is auto-generated during the composer install
parameters:
    database_host: ${DB_HOST}
    database_port: 3306
    database_name: ${DB_NAME}
    database_user: ${DB_USER}
    database_password: ${DB_PASS}
    mailer_transport: smtp
    mailer_host: 127.0.0.1
    mailer_user: null
    mailer_password: null
    secret: ThisTokenIsNotSoSecretChangeIt
    mail_from_email: null
    mail_from_name: null
    portal_url: null
    portal_asset_url: null
    wkhtmltopdf_binary: /usr/local/bin/wkhtmltopdf.sh
    sendgrid_api_key: ${SENDGRID_KEY}

解决方案 #

• 确保环境变量传入容器：parameters.dist中使用的${DB_HOST}等环境变量需要在app容器中存在。可以在docker-compose.yml的app服务的environment字段中添加这些变量：

  environment:
    # 原有环境变量...
    DB_HOST: "你的RDS端点地址"
    DB_NAME: "目标数据库名"
    DB_USER: "数据库用户名"
    DB_PASS: "数据库密码"
    SENDGRID_KEY: "你的SendGrid密钥"
  

  也可以在docker-compose所在目录创建.env文件，写入这些变量，docker-compose会自动加载该文件的环境变量。

• 验证Symfony加载的参数是否正确：进入app容器执行以下命令，查看实际加载的数据库主机配置：

  php bin/console debug:container --parameter=database_host
  

  如果返回的不是正确的RDS端点，说明参数未正确替换。需要执行composer install生成parameters.yml文件，或者执行php bin/console cache:clear --env=prod清除生产环境缓存，确保参数被正确加载。

• 测试PHP环境的DNS解析能力：虽然mysql命令行能解析RDS域名，但PHP的DNS解析可能存在问题。在容器中创建测试脚本test_dns.php：

  <?php
  $host = getenv('DB_HOST');
  var_dump(gethostbyname($host));
  ?>
  

  执行php test_dns.php，如果返回错误，说明PHP环境的DNS配置异常。可以在app服务的docker-compose配置中添加DNS服务器：

  dns:
    - 8.8.8.8
    - 1.1.1.1
  

• 确认RDS安全组规则：检查RDS实例的安全组入站规则，是否允许容器的出口IP访问3306端口。可以在容器中执行curl ifconfig.me获取公网IP，然后将该IP添加到RDS安全组的入站规则中。

内容的提问来源于stack exchange，提问作者sakisk