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I'm trying to understand the (more than) various EC2 options at Amazon AWS.

In the documentation, they describe what each utilization type is best suited for, along with what hardware the instance will run on (small, large, extra large).

What I want to know is what is the technical difference between the different utilization types? What am I really buying?

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3 Answers

This is an issue of confusion for many people.

There is no technical difference - an m1.large instance is an m1.large instance, whether it's a heavy, medium, or light utilization reserved instance.. The difference is all in how you're billed.

If you plan on a specific instance being on 24x7, then get the heavy utilization instance. If the server won't be powered on 24x7, then either the medium or light usage instances would be appropriate.

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As explained here:


It's a billing issue only. Assuming a 1-year reservation, if you plan to use the instance N% of hours in the year, you should use:

0-32% On-Demand or Spot
33-49% Light
50-85% Medium
86-100% Heavy

to spend the least on the instance over the course of the year.

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See my answer here. I think it explains the difference quite well.

Amazon EC2 Reserved Instances: "Heavy Utilization" clarification

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