How to Resize and Change Instances in AWS

Posted by Staff   |   Wednesday, July 15th, 2015

This is a guest post by Debra Shinder.

Moving some or all of your company’s resources into the cloud is a big decision, and it’s important that you carefully formulate a plan before you leap in. Regardless of how well thought out your plan is, however, sometimes things change, and you might discover that you need to make changes to your cloud configuration. Depending on your cloud provider, the changes that you want to make after the fact might be easy to do, difficult, or not doable at all.

If your organization has selected Amazon Web Services as your cloud provider, there are a number of changes that you can make to your Elastic Cloud Computing (EC2) virtual servers, which in AWS parlance are called instances. For example, when you set up your instances, a couple of the choices that you have to make are the type and size of the instance. The type (T2, M3, C4, C3, R3 and so forth) indicates the purpose (that is, general purpose vs. optimized for specific types of load and performance). The size refers to the number of virtual CPUs and amount of memory and storage available to the instance.

Reserved instances can, in some cases, be changed to a different instance type if there is sufficient capacity and making the change doesn’t change the overall footprint. You could divide a reservation for one large instance into multiple small ones or combine four small ones into one large one – again, so long as the footprint remains constant. It’s also possible to upgrade or downgrade your instance type as long as you stay within the same instance family.

If your instance root device is an Elastic Block Storage (EBS) volume, you can resize the instance by changing the instance type, but if the root device is an instance store volume (created from a template in Amazon S3), then you have to migrate to a new instance in order to change the size. If you don’t know what the root device is, you can find out by clicking Instances in the EC2 console, selecting the instance for which you want information, and clicking Root Device Type in the details pane.

Other changes that you might want to make include moving your reservation to a different availability zone within the same region or changing the network platform of some or all of your reserved instances (EC2 classic to EC2-VPC or the other way around).

There are two ways to make these changes. You can submit a Modification Request to Amazon using the Modify Reserved Instances page within the Amazon EC2 console, which is accessible from the Reserved Instances page. Here you’ll see that you have the following choices:

  • No change
  • Change the availability zone
  • Change the network platform
  • Change the instance type

To make a change, click Add and select the change you want to make. You can delete a configuration you selected by clicking the X on that row. You need to click Submit Modifications in order to complete the process. You’ll get a message that the request is being processed, and you’ll be notified that your request is pending modification.

Note that this doesn’t mean the request will be granted. It could still fail if there isn’t sufficient capacity, or you could receive an error in processing if the details of your reserved instances don’t match or the target configurations for all of the subsets of the reserved instances you’re modifying aren’t unique.

It is also possible to use programming tools to programmatically make the modifications you desire, using the AWS command line interface, the EC2 command line interface, the EC2 API and the AWS SDK for Java.

If you’re just about to get started with AWS or you’re still considering whether to go with Amazon as your cloud services provider, check out my two part overview of Amazon Web Services over on here.