VMs started shutting down after 1 hour by itself automatically and on vCenter you start to see memory status changes.
From the above, you see that memory state changes. The first thing most people thought was there must be some issue or misconfiguration on the vSphere portion.
Further checks and view, the host and VM seems to be healthy and this is affecting a majority of VMs. Further isolation, all these were running Microsoft Windows.
The first thing I wanted to confirm was to run a VM that is non-windows to make sure this is not due to OS issue. Instead of installing one, you can use a tiny VM version small and won't take up much resource from here.
The VM runs normal and nothing happens. This confirmed is not a vSphere issue but more of a OS related problem. So a check on the license activation is required. And indeed confirmed license has expired and not activated.
We experience this in our ASEAN demo lab with our Active Directory shutting down and similar problem and this is all mentioned in Microsoft knowledge base. For Windows 2008 R2 & Windows 7 refer to this KB for Windows 2012 refer to this KB. From the field, the reported time for Windows 7 & Windows 8 automatic restart within 1 hour while Windows 2012 is 30 minutes.
If this happens on a physical server, we would likely not suspect a hardware failure since it was able to run normally. Instead we will be troubleshooting in the OS. So why in virtualized environment we start to investigate on the virtualization layer when all was good?
We start to forget the main place to start. With or without virtualization, we should always find out more from one area and isolate it rather of jumping straight to an area that hasn't done any harm but showing your more information.
This do not change very much and I hope this give everyone a clearer picture that something things happen just very near to us but we have jump to conclusion too far away.