MSDN Magazine - April 2008 - (Page 11)

Logging Web App Errors, Learning LINQ, and More SCOTT MITCHELL Log and Review Web Application Errors In a perfect world there would be no errors in production. Database and Web servers would never go down, and code would be thoroughly tested and designed to gracefully handle any situation or input that might otherwise have caused an error. But we program in reality, where deadlines and never-ending feature requests are a constant and where database and Web servers can and do go offline. When errors occur in a production environment, it is essential that the details be logged and the development team promptly notified. There are two common solutions for logging errors in an ASP.NET application: the ASP.NET health monitoring system and Atif Aziz’s Error Logging Modules and Handlers (ELMAH). Both systems enable page developers to programmatically log the details of an error to a specified log source. Moreover, both offer mechanisms for automatically logging unhandled exceptions. The health monitoring system from Microsoft is a robust, low-level framework that was introduced with ASP.NET 2.0. In addition to monitoring errors, it is capable of recording a variety of other metrics—including application lifecycle events such as application startup and shutdown, request-level events, and security-related events that include authorization violations and successful and failed login attempts. When a monitored event occurs, it can be logged to any number of specified logging sources. The logging functionality in the health monitoring system is built atop the provider model, enabling developers to plug in a custom logging provider or to use any of the built-in Error Log in ELMAH providers. Among the built-in providers, there is one that records event details to the Windows Event Log, another that writes the event to a SQL Server database, and one that sends the details to an e-mail address. To begin using health monitor, simply add the appropriate configuration markup to the application’s web.config file. The health monitoring configuration information must include the events to monitor, the logging providers, and how each monitored event is to be logged. In addition to this basic information, the configuration markup can also include options such as whether the logging should be buffered, the minimum number of times an event must occur before logging commences, and the maximum number of times a given event should be recorded before future instances are ignored. The other common logging option, ELMAH, is a set of open source HTTP ® handlers and modules. So while the ASP.NET health monitoring system can monitor a variety of events, ELMAH was designed to only log application errors. When an error occurs, ELMAH logs the details to a specified logging provider and, optionally, sends an e-mail to a configurable set of recipients. There are a number of built-in and community-created ELMAH logging providers, including some that log to an XML file, to a SQL Server database, to an Oracle database, and to the SQLite database (a lightweight, open source database engine). ELMAH has some interesting display capabilities and supports all versions of ASP.NET. The ASP.NET health monitoring system does not provide any functionality for reviewing the logged events, but ELMAH includes built-in HTTP handlers that can display the error log from a Web page or as an RSS feed. And while health monitoring only works with ® april2008 11

Table of Contents Feed for the Digital Edition of MSDN Magazine - April 2008

MSDN Magazine - April 2008 Contents Toolbox CLR Inside Out Basic Instincts Cutting Edge Foundations Test Run Service Station Windows with C++ Going Places { End Bracket }

MSDN Magazine - April 2008

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