An Amazon EC2 instance running Windows loses network connectivity intermittently, causing the instance to become inaccessible. When this occurs, the instance must be restarted or rebooted to restore network connectivity. Additionally, Windows scheduled tasks might fail to start or stop at the expected time.

These problems can occur if the Windows Time service is not configured with the correct local time. When this happens, DHCP lease times can be inaccurate, which can cause causing networking problems with TCP/IP address lease expiration. Incorrect local time can also prevent Windows scheduled tasks from running at their scheduled times. The Windows Time service can be configured incorrectly under the following conditions:

  • EC2 instances running Windows Server 2008 and later set their local time to UTC time in the absence of the registry key RealTimeIsUniversal. As a result, an instance of Windows located in a time zone other than the UTC time zone is configured with the incorrect local time.
  • EC2 Windows instances that use the Citrix Paravirtual (PV) Drivers can experience time synchronization problems caused by the Citrix Xen Guest Agent service.
  1. Add the RealTimeIsUniversal registry key to the instance by following the steps at Configuring Time Settings for Windows Server 2008 and later. This key configures Windows to synchronize time settings with the CMOS clock rather than with UTC time.
  2. If your EC2 instance is using a version of the file C:\Program Files\Citrix\XenGuestAgent.exe with a modified date earlier than March 12, 2013, follow the steps at Upgrading Your Citrix Xen Guest Agent Service.
  3. For more information about use of the registry key RealTimeIsUniversal, see High CPU usage during DST changeover in Windows Server 2008, Windows 7, or Windows Server 2008 R2.

EC2, Windows Server, connectivity, UTC, scheduled tasks, Citrix, XenGuestAgent, DHCP, RealTimeIsUniversal


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Published: 2015-12-31