Need help on how to monitor IIS? This guide covers how to cover the basics including HTTP ping checks, IIS Application Pools, and important Windows Performance Counters. We also take a look at how to use an application performance management system to simplify all of this and get more advanced IIS performance monitoring for ASP.NET applications.

IIS Performance Monitoring Topics:

• Ensuring your IIS Application is running
• Windows performance counters for IIS & ASP.NET
• Advanced IIS performance monitoring for ASP.NET

How to Monitor if Your IIS Application is Running

The first thing you want to do is setup monitoring to ensure that your application is running.

Website Monitor via HTTP Testing

One of the best and easiest things you can do is set up a simple HTTP check that runs every minute. This will give you a baseline to know if your site is up or down. It can also help you track how long it takes to respond. You could also monitor for a 200 OK status or if the request returns specific text that you know should be included in the response.

Monitoring IIS via a simple HTTP check is also a good way to establish a basic SLA monitor. No matter how many servers you have, you can use this to know if your web application was online and available.

Here is an example of one of our HTTP checks we use against Elasticsearch to help with monitoring it. We do this via Retrace; you could also you tools like Pingdom. In this example, we receive alerts if the number_of_nodes is not what we are expecting or if it doesn’t find an HTTP status of 200 OK.

Ensure Your IIS Application Pool is Running

If you have been using IIS very long, you have probably witnessed times when your application mysteriously stops working. After some troubleshooting, you may find that your IIS Application Pool is stopped for some reason, causing your site to be offline.

Sometimes an IIS Application Pool will crash and stop due to various fatal application errors, issues with the user the app pool is running under, bad configurations, or other random problems. It is possible to get it into a state where it won’t start at all due to these type of problems.

It is a good best practice always to monitor that your IIS Application Pool is started. It runs as w3wp.exe. Most monitoring tools have a way to monitor IIS Application Pools. Our product, Retrace, monitors them by default.

One weird thing about app pools is they can be set to “Started” but may not actually be running as w3wp.exe if there is no traffic to your application. In these scenarios, w3wp.exe may not be running, but there is no actual problem. This is why you need to monitor it via IIS’s status and not just look for w3wp.exe to be running on your server.

Recommended Performance Counters for IIS Monitoring

One of the advantages of using IIS as a web server is all of the metrics available via Windows Performance Counters. There is a wide array of them available between IIS, ASP.NET and .NET. For this guide on IIS performance monitoring, I am going to review some of the top Performance Counters to monitor.

To simplify things a bit, I am going to split the Performance Counters up between IIS and ASP.NET particular Performance Counters. All of these are monitored by default as part of Retrace’s application metrics monitoring.

System/Process Counters

• CPU %: The overall server and CPU usage for your IIS Worker Process should be monitored.
• Memory: You should consider tracking the currently used and available memory for your IIS Worker Process.

IIS Performance Counters

• Web Service – Bytes Received/Sec: Helpful to track to identify potential spikes in traffic.
• Web Service – Bytes Sent/Sec: Helpful to track to identify potential spikes in traffic.
• Web Service – Current Connections: Through experience with your app you can identify what is a normal value for this.

ASP.NET Performance Counters

• ASP.NET Applications – Requests/Sec: You should track how many requests are handled by both IIS and ASP.NET. Some requests, like static files, could only be processed by IIS and never touch ASP.NET.
• ASP.NET Applications – Requests in Application Queue: If this number is high, your server may not be able to handle requests fast enough.
• .NET CLR Memory – % Time in GC: If your app spends more than 5% of its time in garbage collection, you may want to review how object allocations are performed.

ASP.NET Error Rate Counters

• .NET CLR Exceptions – # of Exceps Thrown: This counter allows you track all .NET exceptions that are thrown even if they are handled and thrown away. A very high rate of exceptions can cause hidden performance problems.
• ASP.NET Applications – Errors Unhandled During Execution/sec: The number of unhandled exceptions that may have impacted your users.
• ASP.NET Applications – Errors Total/Sec: Number of errors during compilations, pre-processing and execution. This may catch some types of errors that other Exception counts don’t include.

Advanced IIS Performance Monitoring for ASP.NET

Some application monitoring tools, like Retrace, are designed to provide holistic monitoring for your ASP.NET applications. All you have to do is install them, and they can auto detect all of your ASP.NET applications and automatically start monitoring all the basics. Including key Performance Counters and if your IIS Site and Application Pool are running.

Retrace also does lightweight profiling of your ASP.NET code. This gives you code-level visibility to understand how your application is performing and how to improve it.

Benefits of advanced application performance monitoring (APM):

• Track performance of every ASP.NET web request in your application
• Advanced error monitoring and tracking
• Identify slow SQL queries
• Understand the performance of application dependencies including web services, caching, queuing, etc
• View code level transaction traces