Service Unavailable - Recycle an IIS Application Pool and Isolate the Potential Causes of an Application Pool Crash

How to Recycle an IIS Application Pool and Isolate the Potential Causes for an Application Pool Crash

 If you receive an HTTP Error 503 message, it is highly likely that your IIS application pool has stopped. 

There are two common causes for this issue:
  1. Your website is sustaining an extremely high amount of CPU which could significantly impact the performance of your server.  In order to protect the stability of the server, the website was recycled (restarted).  During the recycle, you will receive "Service Unavailable", however, the website will reactivate itself shortly.
  2. Your website has hard-crashed multiple times in rapid succession which has triggered Rapid Fail Protection.  Rapid Fail Protection is a feature in IIS that monitors your website for hard-crashes, and if a certain number of errors occurs in a certain amount of time, it will deactivate the website.  If the website hard-errors more than 5 times in 5 minutes, this indicates that the website is most likely malfunctioning and will need to be manually reactivated by following the workaround below.
If you are receiving the Service Unavailable error because of high CPU utilization
  • Upgrade to a hosting plan that is more in line with your needs
  • Disable the component that is causing the CPU spike or hard-crashes. The component can usually be quickly identified by looking at the most recent DotNetNuke event log entries as well as the most recent DotNetNuke scheduled task executions.
    • To view the site log, login as host. Click on Admin > Site Log. Change Report Type to Detailed Site Log.
    • To view the scheduled tasks, login as host. Click Host > Schedule.
A quick workaround to get your site back up is as follows:
  1. Log into your Control panel
  2. Go to System > Domain > click on your domain.
    • In Plesk 9, in the Additional Tools section click on IIS Application Pool.
    • In Plesk 11, in the My Subscriptions section click on your domain. Choose the Websites and Domains tab. Click on Show Advanced Operations > Dedicated IIS Application Pool for Your Websites.
    • In Plesk 12: In My subscriptions, click your domain, and choose websites and domains tab at the top. Click show more in the middle of the domain controls at the bottom, and select Dedicated IIS application Pool for your websites and then click recycle
    • In Plesk 12.5: In My subscriptions, click your domain, and choose websites and domains tab at the top. Select Dedicated IIS application Pool for your website and then click recycle
  3. Click Start if it is stopped or Recycle if it is not grayed out.
  4. This should recycle your IIS application pool and bring your website back online. Note: The best place to recycle an application pool is through IIS itself. If your site does not come back online and you do not have access to IIS (you are in a shared hosting environment), contact the support team for assistance.
  5. If this continues to happen and the underlying cause can not be determined, you may request that Rapid Fail Protection be disabled on your site.  Rapid Fail Protection must be disabled through IIS by following these procedures:
Disable Rapid Fail Protection through IIS.
This is a temporary fix. The issue that is causing Rapid Fail Protection to stop the application pool should be investigated and corrected. If you are a shared hosting client, you will need to open a support ticket to make this request. Dedicated server clients can perform the following steps:
  1. Open up IIS by clicking Start > Administrative Tools > Internet Information Services (IIS) Manager
  2. Click on the "+" sign to expand the server in the top of the left navigation pane.
  3. Click on Application Pools 
  4. Right-click on the appropriate application pool and select Properties in IIS 6 or Advanced Settings in IIS7
    1. In IIS 6 click on the Health tab and uncheck Rapid Fail Protection
    2. In IIS 7 scroll down to the Rapid-Fail Protection section. Change Enabled to False.
  5. Click OK to save the settings.
Stopped App Pool

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