How can I resolve the following problems that occur on an Amazon EC2 instance running Windows Server after applying the RealTimeIsUniversal registry entry for the instance?

  • On an EC2 instance running Windows Server 2008 or Windows Server 2008 R2 from an AMI created before February 22, 2013, the RealTimeIsUniversal key can cause 100% CPU utilization during time changes that occur for Daylight Saving time and during time changes that occur at the start of each calendar year (January 1).
  • On an EC2 instance running Windows Server 2008 R2 from an AMI created before February 22, 2013, the RealTimeIsUniversal key can block changing the system time when using Windows Control Panel.

To be sure that your Amazon EC2 instance of Windows Server maintains the correct local time, you might need to apply the RealTimeIsUniversal registry entry. However, this registry entry can cause side effects if the associated AMI was created before February 22, 2013. These side effects can vary, depending on which version of Windows Server your EC2 instance is running.

The problems described are known issues that Microsoft has addressed with hotfixes for those customers experiencing the specific problems described after setting the RealTimeIsUniversal registry key.

Note: This hotfix requires Service Pack 1 to be installed on each of the Windows Server versions listed in the Applies To section at the bottom of the article. This hotfix is also referenced as the fix for the issue described in High CPU usage during DST changeover in Windows Server 2008, Windows 7, or Windows Server 2008 R2.


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Published: 2016-02-23

Updated: 2018-07-30