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I have 4 reserved instances with a few months left:
c1.medium (active)
m1.small (active)
m1.small (active)
t1.micro (active)

In "My Instances" i see 5 stopped instances, and 4 running:

In the billing section, it's clear that i am billed for the running instances:

Amazon EC2 running Windows Reserved Instances:
c1.medium (17 hrs)
m1.small (1270 hrs)
Amazon EC2 running Windows:
m1.large (640 hrs)
c1.medium (665 hrs)

Problem is, i can't seem to move the working machines to the reserved instances (it suggests only "on demand" and "spot" instances...)

what is the best approach for utilizing the already paid for (and cheaper) reserved instances?
How do i do that?

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This question is off-topic under current topicality rules. – HopelessN00b Jan 21 '15 at 21:35
Amazon offer free support around billing. Ask them. – Tim Feb 19 at 4:32

Your instances should automatically take advantage of reserve if there are reserves available.

However, you have to remember that reserve comes with a number of limitations - when you buy reserve they are locked to

  1. Instance type
  2. Availability zone and region
  3. Operating system

If your instances are in a different AZ, for example, from what you bought, they won't take advantage of reserve pricing.

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Thanks - but should i do now? shall i shut down a server, and the next time i create an instance it'l use the reserved one? – seldary May 1 '11 at 8:40
@seldary correct, if you bring it up in the right size/type/az. You can actually change instance types with a stop and start now, but I think have to terminate/create to move AZs. – Ernest Mueller May 2 '11 at 18:13

Reserved instances are still on-demand instances, they have an hourly charge. That hourly charge is just cheaper than for a non-reserved on-demand instance.

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Thanks - i know, but i am paying a higher hourly rate for an on-demand instance, while a cheaper reserved instance is lying around doing nothing... – seldary Apr 28 '11 at 13:50

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