Chapter 4: Troubleshoot and debug web applications

Prevent and troubleshoot runtime issues

• Troubleshooting performance, security and errors

• using performance wizard (Vs2012)
• Using VS profiler (Analyzer | Profiler)
• Using Performance Monitor
• NLog/log4net for logging
• Tracing, Trace.WriteLine("Message")/Write/WriteIf/WriteLineIf

<configuration>
  <system.diagnostics>
    <trace autoflush="false" indentsize="4">
      <listeners>
        <add name="myListener" type="System.Diagnostics.TextWriterTraceListerner" initializeData="TracingInfo.log" />
        <remove name="Default" />
      </listeners>
    </trace>
  </system.diagnostics>
</configuration>

• Error logging
  • HandleErrorAttribute
  • overriding controller's OnException: protected override void OnException(ExceptionContext pContext)
• Enforcing conditions by using code contracts

internal Article GetArticle(int pId)
{
  System.Diagnostics.Contracts.Contract.Requires(id > 0);
  System.Diagnostics.Contracts.Contract.Ensures( Contract.Results<Article>() != null );
  /// some work here
}

[ContractInvariantMethod]
protected void ManageInvariant()
{
  System.Diagnostics.Contract.Invariant(this.Id < 0 );
}

* Preconditions
* Invariants
* Postconditions

install Code Contracts Editor Extensions from VS Gallery

• Enabling and configuring health monitoring
  • bufferModes
  • providers
  • profiles
  • rules
  • eventMappings

Design an exception handling strategy

• Handling exceptions across multiple layers
• use Application_Error in Global.asax to handle error pages
• set error information in Web.config as below:

  <customErrors mode="RemoteOnly" default_redirect="ErrorManager/ServerError">
    <error statusCode="400" redirect="ErrorManager/Status400" />
    <error statusCode="403" redirect="ErrorManager/Status403" />
    <error statusCode="404" redirect="ErrorManager/Status404" />
  </customErrors>

HTTP 500 erros are generally handled by filters or OnException handlers.

set in <system.webServer> of Web.config

• Handle first exception

  AppDomain.CurrentDomain.FirstChanceException += OnFirstChanceException;

  protected void OnFirstChanceException(object sender, System.Runtime.ExceptionServices.FirstChanceExceptionEventArgs e)
  {
  }

Test web application

• running unit tests
  • creating mocks by Fakes Assembly (shim/stub)

  using(ShimsContext.Create())
  {
    System.Fakes.ShimDateTime.NowGet = () => new DateTime(2010,1,1);
    TestMethodNow();
  }

Debug a Windows Azure application

• use IntelliTrace
• use Remote Desktop