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Amazon EC2 lets users reserve EC2 instances. When a Reserved Instance is created, it is valid only for instances of the specific instance type (i.e. m1.Medium) and zone (i.e. us-east-1d). How can I be sure when launching a new instance that I am selecting the correct Type and Zone so that the reserved instance will be used?

Note that I did find a similar question but it seems that question is asking (and indeed, the answer fits) how to be sure that an already running instance is using the Reserved Instance. My question is how to start a new instance such that I can be sure that it will use a Reserved Instance. There are many instance types to choose from with similar names (m1.Medium, m2.Medium, m2.Micro), and there are many "sub zones" that are easily confused (us-east-1b, us-east-1c, us-east-1d). At best the use must open two windows so that he could meticulously compare his available reserved instances with the options on the Launch Instance screen.

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up vote 1 down vote accepted

There is no way to ensure this, but you don't reserve instances at random and presumably you had a reason to reserve one of a particular size in a particular region so you're unlikely to get it wrong.

You could even do it the other way round: launch the instance then reserve one of the same type soon after while it is fresh in your mind - AWS will ensure the reservation applies to any existing instances of the correct type.

If you really want to be sure you are matching them up the two window approach seems to be as good as any, but even if you get it wrong you can just shut down the instance and start a new one of the correct type for a cost of a few cents.

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Accepted for the second paragraph. Thank you ianjs. –  dotancohen Apr 18 '13 at 8:11

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