CentOS rebooted by unknown reason

Hi,

One of my virtual machines (CentOS) had been rebooted WITHOUT any notice.

In /var/log/message, I could find the following message.

WHO or WHAT does reboot it? And why?

Also, is it usual in Azure to be rebooted without any notice?

Actually, I think it's serious problem.

Please investigate it. 

FYI, my subscription is PAY-AS-YOU-GO.

BR,