Basic Application Pool Troubleshooting

This article covers some basic steps to troubleshoot issues with application pools within Microsoft®
Internet Information Services (IIS).

Recycle application pools

Take this troubleshooting step when there is a general application pool error, or the site itself shows poor

By default, recycling an application pool has no ill effect on the website and doesn't bring the site down.
However, if you have any third-party software that integrates with IIS, reach out to the provider of that
software to make sure recycling the application pool does not cause any detrimental effects or downtime to
your site.

Use the following steps to recycle the application pools:

  1. Open the IIS Manager by going to the Start menu and searching for IIS or typing inetmgr.
  2. Select Application Pools.
  3. In the Actions tab, click Recycle. You can also right-click Actions and select Recycle.

Change the application pool recycle settings

Do this step if you have conflicts in performance or with the software on the server at certain times. All
application pools have a default time they recycle. If this recycle conflicts with anything or you see a particular
error at a certain time of day that coincides with the recycle, you can change it by performing the following steps:

  1. Open IIS Manager, expand the Application Pools folder, and select the one you want to edit.
  2. On the Actions panel, select Recycling.
  3. In Edit Application Pool Recycling Settings, select one of the options within the Fixed Intervals
    section, type the values you need, and click Next.
  4. Optionally, go to the next page is labeled Recycling Events to Log. This page allows you to select the
    configurable recycling events and runtime events that you want IIS to send to the Event Log when they occur.
  5. Click Finish.

Change the application pool queue-length limit

Use this option when connection issues with a Client Request 503 error occur. This error occurs when the
number of queued requests exceeds the current queue-length limit. You can check the Event Viewer logs to see if this error occurred. Use the following steps:

  1. In the IIS Manager, expand the Application Pools folder and right-click the application pool.
  2. Click Properties.
  3. Click the Performance tab.
  4. In the Request Queue Limit section, select Limit the Kernel request queue.
  5. Click OK.

Configure rapid-fail protection

IIS might generate a 503 error and initiate rapid-fail protection because the application pool has too many worker processes assigned to the pool that have become unhealthy in a certain period of time. The following steps help to increase the number of failures or the time period before rapid-fail protection initiates, which can help you to clear this error:

  1. Open IIS Manager, expand Local Computer, and then expand Application Pools.
  2. Right-click Application Pools and then click Properties.
  3. Click the Health tab.
  4. In the Failures box, type the number of failures you want before disabling the worker process.
  5. In the Time period box, type the number of minutes during which failure totals are gathered.
  6. Click OK.