How to purchase a Reserved Instance to cover for an existing AWS EC2-VPC instance in eu-west-1

Question

We have an EC2 t2.xlarge instance in eu-west-1 region, for which we wish to purchase a Reserved Instance (RI).

The EC2 reservations we had purchased previously in us-east-1, are of type "Linux/UNIX (Amazon VPC)".

But for eu-west-1 it looks like "Linux/UNIX (Amazon VPC)" type reservations are not available; only available option is "Linux/UNIX" - confirmed by the output (removed for brevity) of the following AWS CLI command:

aws ec2 describe-reserved-instances-offerings \
--region eu-west-1 \
--offering-class standard \
--instance-tenancy default \
--offering-type "All Upfront" \
--instance-type t2.xlarge \
--product-description "Linux/UNIX (Amazon VPC)" \
--filters \
Name=scope,Values="Region" \
Name=duration,Values=31536000

So we are concerned: will purchasing a "Linux/UNIX" reservation slot, allow us to cover ("match") our existing t2.xlarge instance?

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Based on AWS documentation:

Determining Whether You Are Using the EC2-VPC or EC2-Classic Platform (from RDS docs, but offers a decent explanation of EC2-Classic vs EC2-VPC):

Accounts that only support the EC2-VPC platform have a default VPC

You can create a VPC on the EC2-Classic platform, but one is not created for you by default

Our AWS account has a default VPC in eu-west-1 - which leads us to believe that it is of EC2-VPC type.

AWS CLI: aws ec2 describe-reserved-instances-offerings help:

Instances that include (Amazon VPC) in the product platform description ... are for use with Amazon VPC.

My EC2 Reserved Instance isn't applying to my billing—why?

Your RI must exactly match a running EC2 instance’s characteristics. A running instance must match the type, Availability Zone, platform, and tenancy of your RI exactly.

So, based on the above, purchasing a RI offering with "Linux/UNIX" (non-VPC) platform (which is the only available option) may not match/cover our existing (EC2-VPC) instance in eu-west-1.

Can anybody prove me wrong - or suggest an approach to secure a RI (or a comparable billing advantage) for our instance in eu-west-1?

---

We did contact AWS Support - but only got back vague responses like "your RI must exactly match the configurations of your existing instance".

Answer 1

Yes, Linux/UNIX RI is what you need.

In the past AWS used to have EC2 Classic instances that didn’t live in a VPC. Then they introduced VPCs and VPC EC2 instances. Hence in some of the old regions you still have the choice of VPC or Classic RI.

Newer regions never supported EC2 Classic, the only option for EC2 is VPC. Therefore Linux/UNIX RI in those regions means Linux/UNIX (Amazon VPC).

Go ahead, that’s the Reserved Instance type you need.

Hope that helps :)

Answer 2

Rather than using reserved instances you should look into AWS Savings Plans. Basically, you commit to a spend level, and you get a discount based on that. It's simpler and more flexible than reserved instances.

Savings Plans is a flexible pricing model that provides savings of up to 72% on your AWS compute usage. This pricing model offers lower prices on Amazon EC2 instances usage, regardless of instance family, size, OS, tenancy or AWS Region, and also applies to AWS Fargate and AWS Lambda usage.

Savings Plans offer significant savings over On Demand, just like EC2 Reserved Instances, in exchange for a commitment to use a specific amount of compute power (measured in $/hour) for a one or three year period. You can sign up for Savings Plans for a 1- or 3-year term and easily manage your plans by taking advantage of recommendations, performance reporting and budget alerts in the AWS Cost Explorer.