...
In the above data, items 2, 4 and 6 are static (or near static), the others are dynamic, changing at run time.
The system watches for the above data.
Periodically (configurable, such as every minute), check the system checks whether we need to scale up, and whether we need to scale down. These 2 checks can be done in parallel, but if in parallel, need so, the system needs to protect and synchronize the shared data, such as the list of running VMs.
...