Docker容器中ASP.NET Core无法连接AWS RDS MySQL公网数据库

问题背景 #

我有一个ASP.NET Core Web API，需要连接AWS RDS上的公有MySQL实例（带公网IP）。用MySQL Workbench和本地HTTP模式运行应用时，都能正常连接数据库；但Docker启动应用后，API本身可以正常运行，却无法连接数据库。连接代码使用Dapper实现：

db = new MySqlConnection(masterConnection);
await db.OpenAsync();

报错信息 #

MySqlConnector.MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts.
   at MySqlConnector.Core.ServerSession.OpenTcpSocketAsync(ConnectionSettings cs, ILoadBalancer loadBalancer, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 1146
   at MySqlConnector.Core.ServerSession.ConnectAsync(ConnectionSettings cs, MySqlConnection connection, Int32 startTickCount, ILoadBalancer loadBalancer, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ServerSession.cs:line 438
   at MySqlConnector.Core.ConnectionPool.ConnectSessionAsync(MySqlConnection connection, String logMessage, Int32 startTickCount, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 403
   at MySqlConnector.Core.ConnectionPool.ConnectSessionAsync(MySqlConnection connection, String logMessage, Int32 startTickCount, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 408
   at MySqlConnector.Core.ConnectionPool.GetSessionAsync(MySqlConnection connection, Int32 startTickCount, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 98
   at MySqlConnector.Core.ConnectionPool.GetSessionAsync(MySqlConnection connection, Int32 startTickCount, Activity activity, IOBehavior ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/Core/ConnectionPool.cs:line 128
   at MySqlConnector.MySqlConnection.CreateSessionAsync(ConnectionPool pool, Int32 startTickCount, Activity activity, Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 929
   at MySqlConnector.MySqlConnection.OpenAsync(Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 423
   at coolco_backend.Data.CollectiblesData.GetCollectiblesByUserId(Int32 idUser) in E:\Apes\Proyectos\coolco-backend\Data\CollectiblesData.cs:line 28
   at coolco_backend.Domain.CollectiblesDomain.GetCollectiblesByUserId(Int32 id) in E:\Apes\Proyectos\coolco-backend\Domain\CollectiblesDomain.cs:line 28
   at coolco_backend.Controllers.CollectiblesController.GetContentByIdUser(Int32 idUser) in E:\Apes\Proyectos\coolco-backend\Controllers\CollectiblesController.cs:line 23
   at lambda_method8(Closure, Object)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 actionResultValueTask)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

排查与解决方案 #

1. 检查RDS安全组与Docker网络IP #

默认Docker使用桥接网络，容器IP与宿主机IP不同。如果RDS安全组仅允许宿主机IP访问，容器会被拦截：

• 临时测试：启动容器时添加--network host参数，让容器共享宿主机网络。若能连接，说明是安全组IP限制问题。
• 永久解决：将Docker容器所在网段（或具体容器IP）添加到RDS安全组的入站规则，开放3306端口。

2. 修正连接字符串 #

本地运行时的localhost或宿主机IP在容器内无效：

• 必须使用RDS的公网域名或公网IP，不要用localhost。
• 进入容器执行ping <RDS域名>，测试DNS解析是否正常；检查连接字符串的端口、用户名、密码是否正确。

3. 测试容器内网络连通性 #

进入容器内部验证网络链路：

• 执行docker exec -it <容器ID> bash（Alpine镜像用sh）。
• 用telnet <RDS公网IP> 3306或nc -zv <RDS公网IP> 3306测试端口连通性。若不通，排查宿主机防火墙、Docker网络规则或RDS安全组。

4. 验证MySqlConnector版本兼容性 #

确保MySqlConnector包版本与RDS MySQL版本匹配，部分新版本可能存在协议适配问题：

• 尝试降级或升级MySqlConnector包，重新构建镜像测试。

5. 补充Docker镜像依赖 #

若使用Alpine等轻量镜像，可能缺少SSL相关依赖：

• 在Dockerfile中添加RUN apk add --no-cache openssl，解决SSL连接失败问题。

内容的提问来源于stack exchange，提问作者D4rWiNS