To ensure the correct time synchronization for VM instances, we strongly recommend that you set an independent time synchronization server for these VM instances. If you have not configured any time synchronization server, the time synchronization mechanism for VM instances with different operating systems are as follows:

  • The internal system time of Linux VM instances will use the host time as clock followed by the operations such as creating, enabling, and rebooting the VM instances. Whether the time of the VM instances either lags behind or goes ahead will take effect.
  • Creating Windows VM instances will automatically read the time of hosts as clock.
  • When the internal system time for Windows VM instances lags behind compared to that of hosts, the internal system time for these Windows VM instances will use the time of these hosts as clock followed by the operations such as enabling and starting the VM instances.
  • When the internal system time of Windows VM instances is ahead of that of hosts, the operations such as enabling and rebooting these VM instances will not read the time of these hosts. The possible cause is related to the Windows licensing policy. For example, after a 180-day trial expires, Windows VM instances will stop every one hour. Time regression will skip off the Microsoft licensing policy.
Note:
  • Generally, the time source of the underlying hosts is defined by the chrony.serverIp.0 = 172.20.0.10 option under the /usr/local/zstack/apache-tomcat/webapps/zstack/WEB-INF/classes/zstack.properties directory (Assume that the time synchronization server is 172.20.0.10).
  • Management nodes will synchronize all hosts to use the same time source. When VM instances are created or enabled, these VM instances will follow the time source of their hosts.