In order to ensure that an EC2 instance running Windows Server maintains the correct local time, you might need to apply the RealTimeIsUniversal registry entry for the instance. This registry entry fulfills its intended purpose but can cause side effects if the associated AMI was created before February 22, 2013. The side effects can vary, depending on which version of Windows Server your EC2 instance is running, as described below.

  • If your EC2 instance is 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 Savings time and during time changes that occur at the start of each calendar year (January 1).
  • If your EC2 instance is running Windows Server 2008 R2 from an AMI created before February 22, 2013, the RealTimeIsUniversal key might prevent you from changing the system time using the Windows Control Panel.

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.

Amazon EC2 instance, Windows Server 2008, R2, high CPU utilization, Daylight Savings time, KB2800213, New Year’s Day, RealTimeIsUniversal, 100%, KB2922223


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Published: 2016-02-23