Sometimes EC2 CloudWatch monitoring shows 100% CPU usage but when you ssh to your instance and try to see it with ‘top’ you can’t understand what is happening. Probably, Amazon is “borrowing” some of your CPU cycles to give to someone else who needs it – this is standard practice for a virtualised environment where physical server resources like RAM usage and CPU cycles are often hugely over-committed.

To check for CPU steal, run top and take a look for the %st value. If this value is anything other than zero, it means your VM’s CPU cycles are being “borrowed”.

More: Understanding CPU Steal Time