Azure 上连接到远程 MySQL 数据库的间歇性问题 EF6

Question

我在 Azure 免费订阅上有一个站点，它是 EF6 上的 C#，连接到远程主机上的 MySQL 数据库。该应用程序将在一段时间内正常运行，但对于经过身份验证的用户，它将在 ObjectDataSource 选择事件上出错，并显示以下内容：

Inner exception information (level 1):
    Exception type: System.Data.Entity.Core.EntityException
    Exception message: The underlying provider failed on Open.

Inner exception information (level 2):
    Exception type: MySql.Data.MySqlClient.MySqlException
    Exception message: Unable to connect to any of the specified MySQL hosts.

Request information:
    Request URL: https://xxx.azurewebsites.net:443/default.aspx
    Request path: /default.aspx
    User host address: 111.111.111.111
    User: xxx
    Is authenticated: True
    Authentication Type: ApplicationCookie
    Thread account name: IIS APPPOOL\xxx

Thread information:
    Thread ID: 24
    Thread account name: IIS APPPOOL\xxx
    Is impersonating: False
    Stack trace:    at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Web.UI.WebControls.ObjectDataSourceView.InvokeMethod(ObjectDataSourceMethod method, Boolean disposeInstance, Object& instance)
   at System.Web.UI.WebControls.ObjectDataSourceView.ExecuteSelect(DataSourceSelectArguments arguments)
   at System.Web.UI.WebControls.ListControl.OnDataBinding(EventArgs e)
   at System.Web.UI.WebControls.ListControl.PerformSelect()
   at System.Web.UI.WebControls.BaseDataBoundControl.DataBind()
   at System.Web.UI.WebControls.BaseDataBoundControl.EnsureDataBound()
   at System.Web.UI.WebControls.DropDownList.LoadPostData(String postDataKey, NameValueCollection postCollection)
   at System.Web.UI.WebControls.DropDownList.System.Web.UI.IPostBackDataHandler.LoadPostData(String postDataKey, NameValueCollection postCollection)
   at System.Web.UI.Page.ProcessPostData(NameValueCollection postData, Boolean fBeforeLoad)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

其他时候，对于未经身份验证的用户，它一开始就不会加载，其中：

    Inner exception information (level 1):
    Exception type: System.Data.Entity.Core.ProviderIncompatibleException
    Exception message: An error occurred accessing the database. This usually means that the connection to the database failed. Check that the connection string is correct and that the appropriate DbContext constructor is being used to specify it or find it in the application's config file. See the inner exception for details of the failure.

Inner exception information (level 2):
    Exception type: System.Data.Entity.Core.ProviderIncompatibleException
    Exception message: The provider did not return a ProviderManifestToken string.

Request information:
    Request URL: https://xxx.azurewebsites.net:443/
    Request path: /
    User host address: 111.111.111.111
    User: 
    Is authenticated: False
    Authentication Type: 
    Thread account name: IIS APPPOOL\xxx

Thread information:
    Thread ID: 64
    Thread account name: IIS APPPOOL\xxx
    Is impersonating: False
    Stack trace:    at System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext context, HttpApplication app)
   at System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers)
   at System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context)
   at System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context)
   at System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext)

或

Thread information:
    Thread ID: 27
    Thread account name: IIS APPPOOL\xxx
    Is impersonating: False
    Stack trace:    at System.Data.Entity.Core.EntityClient.EntityConnection.<OpenAsync>d__8.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Data.Entity.Core.Objects.ObjectContext.<EnsureConnectionAsync>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Data.Entity.Core.Objects.ObjectContext.<ExecuteInTransactionAsync>d__3d`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Data.Entity.Utilities.TaskExtensions.CultureAwaiter`1.GetResult()
   at System.Data.Entity.Core.Objects.ObjectQuery`1.<GetResultsAsync>d__e.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Data.Entity.Utilities.TaskExtensions.CultureAwaiter`1.GetResult()
   at System.Data.Entity.Internal.LazyAsyncEnumerator`1.<FirstMoveNextAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Data.Entity.Infrastructure.IDbAsyncEnumerableExtensions.<FirstOrDefaultAsync>d__25`1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNet.Identity.EntityFramework.UserStore`1.<FindAsync>d__d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNet.Identity.AsyncHelper.RunSync[TResult](Func`1 func)
   at Microsoft.AspNet.Identity.UserManagerExtensions.Find[TUser,TKey](UserManager`2 manager, UserLoginInfo login)
   at TDT.Account.RegisterExternalLogin.Page_Load()
   at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e)
   at System.Web.UI.Control.OnLoad(EventArgs e)
   at System.Web.UI.Control.<LoadRecursiveAsync>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Web.Util.WithinCancellableCallbackTaskAwaitable.WithinCancellableCallbackTaskAwaiter.GetResult()
   at System.Web.UI.Page.<ProcessRequestMainAsync>d__14.MoveNext()

我的连接字符串是这样的：第一个用于身份信息的 ApplicationDbContext，第二个用于 EF 模型：

<add name="IdentityConnection" connectionString="server=xxx.xxx.xx.xxx;user id=xxx;database=xxx;password=Password;persistsecurityinfo=True" providerName="MySql.Data.MySqlClient" /> 
<add name="context" connectionString="metadata=res://*/MyModel.csdl|res://*/MyModel.ssdl|res://*/MyM‌​odel.msl;provider=MySql.Data.MySqlClient;provider connection string=&quot;server=111.111.11.11;user id=xxx;database=MyDB;password=password;persistsecurityinfo=True&quot;" providerName="System.Data.EntityClient" />

因为它是在免费的 Azure 上，你可以免费拥有 10 个站点，我已经将该站点的相同版本上传到另一个 Azure 子域，所以当第一个站点出错时，我检查第二个站点，然后那个站点完美连接到数据库并且应用程序正常加载。有人知道发生了什么吗？它是对多个用户的免费 Azure 订阅的限制，还是一次限制数量的用户/连接？我读到 ClearDB MySQL 有 4 个连接的限制，但是这个 MySQL 是完全独立的，不应该有这些限制。虽然第一个错误时第二个站点确实加载，但如果长时间使用第二个站点也会产生错误。 谢谢

Answer 1

我的一个 Java 服务连接到外部 MySQL 服务器时遇到了类似的问题。我终于在 Azure 技术人员的帮助下解决了这个问题。

如果问题与我的有关 - 它是由 Azure 上用于路由的 SNAT 表引起的，here is a post 详细描述了该问题。

我最终为我们所有的 TCP/IP 套接字连接发送了 keep-alive 数据包。另一种解决方案是分配 PIP 地址，但我不确定您是否可以使用 Azure 网站来做到这一点。

我观察到重新连接到我们的 MySQL 所需的时间变化很大，因此得出的结论是，虽然您的远程服务器认为连接仍处于打开状态，但它不允许来自同一 IP（您网站的 VIP）的流量在 Azure 术语中）在 TCP 级别上。

您可以尝试为您的数据库连接将 keepalive 时间设置为低于 4 分钟（我们的应用设置为 60 秒）：

server=xxx.xxx.xx.xxx;user id=xxx;database=xxx;password=Password;persistsecurityinfo=True;Keepalive=60;

我几乎没有 C# 经验，因此请检查 KeepAlive 选项是否对您的连接器有效。好像是根据this网站。