What is CPU burst?

Question

Amazon has recently announced Micro instances for Amazon EC2. I'm also keep reading about "... allow you to burst CPU capacity when additional cycles are available."

My question is, what does CPU burst mean? I want to know/understand this better.

Any pointers, articles, documentation, etc. on the same are appreciated.

Answer 1

Good question - meanwhile there is more information available regarding this topic:

• Amazon has added a still pretty high level FAQ, see How does a Micro instance compare in compute power to a Standard Small instance?

  At steady state, Micro instances receive a fraction of the compute resources that Small instances do. Therefore, if your application has compute-intensive or steady state needs we recommend using a Small instance (or larger, depending on your needs). However, Micro instances can periodically burst up to 2 ECUs (for short periods of time). This is double the number of ECUs available from a Standard Small instance. Therefore, if you have a relatively low throughput application or web site with an occasional need to consume significant compute cycles, we recommend using Micro instances.

  [Note: ECU is a “EC2 Compute Unit”, see What is a “EC2 Compute Unit” and why did you introduce it? for details]

• The Amazon EC2 User Guide has gained a dedicated, elaborate and especially illustrated chapter on Micro Instances as well, it is a highly recommended read for everybody thinking about using this interesting instance type!

• Finally, Amazon EC2 Micro Instance and Stolen CPU offers an interesting analysis and demonstration how the throttling works, as observed on a micro instance running Ubuntu Linux.

Answer 2

In a nutshell, if the host is not experiencing CPU contention, you'll be able to use more CPU "shares" (for short periods of time) than are normally reserved for your EC2 instance.