Тайм-аут истек -> Невозможно подключиться к любому из указанных хостов MySQL

Я ожидаю очень неприятную проблему и не могу найти причину.

Существует приложение, размещенное на Azure, которое использует MySQL db. Я использую MySQL.Data nuget из Oracle (6.10.5). Очень часто я получаю ошибку с истечением времени ожидания с помощью Невозможно подключиться к любому из указанных узлов MySQL (дюжина в 24 часа).

Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
Exception Details: MySql.Data.MySqlClient.MySqlException: Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.

Трассировки стека:

    [MySqlException (0x80004005): Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.]
   MySql.Data.Common.StreamCreator.GetTcpStream(MySqlConnectionStringBuilder settings) +177
   MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings) +37
   MySql.Data.MySqlClient.NativeDriver.Open() +55

[MySqlException (0x80004005): Unable to connect to any of the specified MySQL hosts.]
   MySql.Data.MySqlClient.NativeDriver.Open() +151
   MySql.Data.MySqlClient.Driver.Open() +50
   MySql.Data.MySqlClient.Driver.Create(MySqlConnectionStringBuilder settings) +225
   MySql.Data.MySqlClient.MySqlPool.CreateNewPooledConnection() +15
   MySql.Data.MySqlClient.MySqlPool.GetPooledConnection() +288
   MySql.Data.MySqlClient.MySqlPool.TryToGetDriver() +93
   MySql.Data.MySqlClient.MySqlPool.GetConnection() +65
   MySql.Data.MySqlClient.MySqlConnection.Open() +629
   SalesManager.Models.ConnectionClass.QueryExec() in C:\Users\Gabinet\Source\Repos\SalesManager\SalesManager\SalesManager\Models\Data\ConnectionClass.cs:39
   SalesManager.Models.ProductDownload.GetStorageQuantity(Int32 id) in C:\Users\Gabinet\Source\Repos\SalesManager\SalesManager\SalesManager\Models\ProductDownload.cs:58
   SalesManager.Controllers.SalesController.Index(String sortOrder, String df, String dt) in C:\Users\Gabinet\Source\Repos\SalesManager\SalesManager\SalesManager\Controllers\SalesController.cs:41
   lambda_method(Closure , ControllerBase , Object[] ) +194
   System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +19
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary'2 parameters) +169
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary'2 parameters) +27
   System.Web.Mvc.Async.AsyncControllerActionInvoker.<BeginInvokeSynchronousActionMethod>b__39(IAsyncResult asyncResult, ActionInvocation innerInvokeState) +24
   System.Web.Mvc.Async.WrappedAsyncResult'2.CallEndDelegate(IAsyncResult asyncResult) +31
   System.Web.Mvc.Async.WrappedAsyncResultBase'1.End() +50
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +33
   System.Web.Mvc.Async.AsyncInvocationWithFilters.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3d() +50
   System.Web.Mvc.Async.<>c__DisplayClass46.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +228
   System.Web.Mvc.Async.<>c__DisplayClass33.<BeginInvokeActionMethodWithFilters>b__32(IAsyncResult asyncResult) +15
   System.Web.Mvc.Async.WrappedAsyncResult'1.CallEndDelegate(IAsyncResult asyncResult) +15
   System.Web.Mvc.Async.WrappedAsyncResultBase'1.End() +50
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +35
   System.Web.Mvc.Async.<>c__DisplayClass2b.<BeginInvokeAction>b__1c() +26
   System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +100
   System.Web.Mvc.Async.WrappedAsyncResult'1.CallEndDelegate(IAsyncResult asyncResult) +15
   System.Web.Mvc.Async.WrappedAsyncResultBase'1.End() +50
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +29
   System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +15
   System.Web.Mvc.Async.WrappedAsyncVoid'1.CallEndDelegate(IAsyncResult asyncResult) +29
   System.Web.Mvc.Async.WrappedAsyncResultBase'1.End() +50
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +36
   System.Web.Mvc.Controller.<BeginExecute>b__15(IAsyncResult asyncResult, Controller controller) +14
   System.Web.Mvc.Async.WrappedAsyncVoid'1.CallEndDelegate(IAsyncResult asyncResult) +22
   System.Web.Mvc.Async.WrappedAsyncResultBase'1.End() +50
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +27
   System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +12
   System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +21
   System.Web.Mvc.Async.WrappedAsyncVoid'1.CallEndDelegate(IAsyncResult asyncResult) +29
   System.Web.Mvc.Async.WrappedAsyncResultBase'1.End() +50
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +29
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +11
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +577
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +157

Azure App Insights дает только тайм-аут:

Event code: 3005

Event message: An unhandled exception has occurred.

Event time: 22/12/2017 14:40:56

Event time (UTC): 22/12/2017 14:40:56

Event ID: 503190c80af54cdb87140fe1f808de22

Event sequence: 16

Event occurrence: 5

Event detail code: 0



Application information:

    Application domain: /LM/W3SVC/41351921/ROOT-1-131584264107173868

    Trust level: Full

    Application Virtual Path: /

    Application Path: D:\home\site\wwwroot\

    Machine name: RD00155D58C141



Process information:

    Process ID: 10784

    Process name: w3wp.exe

    Account name: IIS APPPOOL\xxxx



Exception information:

    Exception type: MySqlException

    Exception message: Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding.
   at MySql.Data.Common.StreamCreator.GetTcpStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.NativeDriver.Open()





Request information:

    Request URL: http://xxxxx.azurewebsites.net/

    Request path: /

    User host address: xx.xxx.xxx.xx

    User: xxxxx

    Is authenticated: True

    Authentication Type: ApplicationCookie

    Thread account name: IIS APPPOOL\xxxx



Thread information:

    Thread ID: 35

    Thread account name: IIS APPPOOL\xxxx

    Is impersonating: False

    Stack trace:    at MySql.Data.Common.StreamCreator.GetTcpStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.Common.StreamCreator.GetStream(MySqlConnectionStringBuilder settings)
   at MySql.Data.MySqlClient.NativeDriver.Open()

Я не могу вызвать эту ошибку на моей локальной машине. Я могу пинговать свой MySql db от Azure. Учетные данные в порядке - он отлично работает на моей локальной машине.

Класс подключения:

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using MySql.Data.MySqlClient;

namespace SalesManager.Models
{
    public class ConnectionClass : IDisposable
    {
        private MySqlConnection _con;
        private MySqlCommand _cmd;
        private MySqlDataAdapter _da;
        private DataTable _dt;

        private string _constr =
            "Server=mysqldb.com; Database=databaseName; Uid=database_user; Pwd=database_pass; Default Command Timeout=300000; ";

        public ConnectionClass()
        {
            _con = new MySqlConnection(_constr);
        }

        public void MySqlQuery(string sqlquery)
        {
            _cmd = new MySqlCommand(sqlquery, _con);
        }

        public void MySqlQueryWithParam(string sqlquery, string paramName, string paramValue)
        {
            _cmd = new MySqlCommand(sqlquery, _con);
            _cmd.Parameters.AddWithValue(paramName, paramValue);
        }

        public DataTable QueryExec()
        {
            _con.Open();
            _da = new MySqlDataAdapter(_cmd);
            _dt = new DataTable();
            _da.Fill(_dt);
            _con.Dispose();
            return _dt;
        }

        public void NonQueryExec()
        {
            _con.Open();
            _cmd.ExecuteNonQuery();
            _con.Dispose();
        }

        public void Dispose()
        {
            _con.Close();
            _con.Dispose();
        }
    }
}

Метод, который не выполняется:

public static int GetStorageQuantity(int id)
{
    if (id != 9999)
    {
        connection = new ConnectionClass();
        string sql = "select quantity from ps_stock_available where id_product = @pId";
            connection.MySqlQueryWithParam(sql, "@pId", id.ToString());
            var dr = connection.QueryExec().Rows[0];
            var quantity = Convert.ToInt32(dr["quantity"].ToString());
            return quantity;
    }
    return 0;
}

Я предполагаю, что у меня отсутствует что-то, связанное с пулом соединений, с которым я не знаком.

Любая идея, что может быть причиной? Что еще можно проверить?

Ваша помощь будет очень признательна!