Docker化C#微服务无法连接同网桥的Docker MySQL问题

问题概述 #

Docker化的C#微服务无法连接同一自定义网桥网络中的Docker化MySQL，报错Unable to connect to any of the specified MySQL hosts。但主机通过MySQL Workbench、本地运行的C#服务均能正常连接该MySQL实例。

配置文件 #

C#服务Dockerfile #

FROM mcr.microsoft.com/dotnet/sdk:6.0 as build
COPY ./User /microservices/User
COPY ./Associated /microservices/Associated
WORKDIR /microservices/User/User.API
RUN dotnet restore
RUN dotnet build -o /app
RUN dotnet publish -o /publish -c Debug
 
FROM mcr.microsoft.com/dotnet/aspnet:6.0 as base
COPY --from=build  /publish /app
WORKDIR /app
ENV ASPNETCORE_URLS=http://+:5114
EXPOSE 5114
ENTRYPOINT ["dotnet", "User.dll"]
# CMD ["./User"]

Docker Compose文件 #

services:
  user_api:
    image: df_user_api:latest
    container_name: user_api
    build:
      context: .
      dockerfile: df_user_api
    ports: [5114:5114]
    depends_on: [mysql]
    networks: [associated]
  mysql:
    image: mysql:latest
    container_name: mysql
    restart: unless-stopped
    environment:
      MYSQL_ROOT_PASSWORD: roottooR1!
      MYSQL_DATABASE: webshop2023
      MYSQL_USER: test
      MYSQL_PASSWORD: test123
      MYSQL_LOG_CONSOLE: "1"
      MYSQL_LOG_ERROR: "/var/log/mysql/error.log"
    ports: [3306:3306]
    networks: [associated]
    volumes:
      - "mysql-data:/var/lib/mysql"
      - "mysql-log:/var/log/mysql"
      - "mysql-conf:/etc/mysql/conf.d"
networks:
  associated:
    name: associated
volumes:
  mysql-data:
    driver: local
  mysql-log:
    driver: local
  mysql-conf:
    driver: local

报错信息 #

fail: Microsoft.AspNetCore.Server.Kestrel[13]
user_api  |       Connection id "0HN006R0TSPN5", Request id "0HN006R0TSPN5:00000004": An unhandled exception was thrown by the application.
user_api  |       MySqlConnector.MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts.

已验证的正常场景 #

• 主机通过localhost:3306，使用MySQL Workbench能正常连接Docker化MySQL
• 本地运行的C#微服务，通过localhost:3306能正常连接该MySQL

使用的连接字符串 #

• 本地环境："server=localhost;port=3306;user=test;password=test123;database=webshop2023"
• Docker网络内："server=mysql;port=3306;user=test;password=test123;database=webshop2023"

排查与解决方向 #

1. 确保MySQL服务完全就绪后再启动C#服务 #

depends_on仅保证容器启动顺序，不确保MySQL服务已初始化完成。添加健康检查确保MySQL就绪：
在Docker Compose的mysql服务中添加：

healthcheck:
  test: ["CMD", "mysqladmin", "ping", "-h", "localhost", "-u", "test", "-ptest123"]
  interval: 5s
  timeout: 5s
  retries: 5

同时修改user_api的depends_on：

depends_on:
  mysql:
    condition: service_healthy

2. 验证MySQL是否监听所有网卡 #

默认MySQL可能仅绑定127.0.0.1，导致容器外同网络无法访问：

• 进入MySQL容器：docker exec -it mysql bash
• 执行命令检查绑定地址：mysql -u test -ptest123 -e "SHOW VARIABLES LIKE 'bind_address';"
• 若结果为127.0.0.1，在mysql-conf卷对应的主机目录下新建my.cnf，添加：

  [mysqld]
  bind-address = 0.0.0.0
  

• 重启MySQL容器：docker restart mysql

3. 检查Docker网络连通性 #

验证C#容器能否访问MySQL容器：

• 进入user_api容器：docker exec -it user_api bash
• 执行ping mysql，确认能解析到IP并连通
• 执行telnet mysql 3306，确认3306端口开放

4. 确认连接字符串正确注入 #

确保Docker化的C#服务确实使用了server=mysql的连接字符串，而非硬编码的localhost：
在Docker Compose的user_api服务中添加环境变量传递连接字符串：

environment:
  - ConnectionStrings__DefaultConnection=server=mysql;port=3306;user=test;password=test123;database=webshop2023

在C#的appsettings.json中配置读取该环境变量，或直接在代码中获取环境变量构建连接字符串。

5. 检查MySQL用户权限 #

确保test用户允许从任意主机（包括容器网络）连接：

• 进入MySQL容器，执行SQL：

  SELECT host, user FROM mysql.user WHERE user='test';
  

• 若host为localhost，执行以下命令更新权限：

  ALTER USER 'test'@'%' IDENTIFIED BY 'test123';
  FLUSH PRIVILEGES;
  

内容的提问来源于stack exchange，提问作者S4UR000N