AWS Reserved Instances size flexibility and Limits

2
votes

We're currently running few m4.large & few t2.medium & t2.small instances (EC2) in our AWS account. We're planning to buy few reserved instances (RI) in our accounts. I went to AWS Blog - New – Instance Size Flexibility for EC2 Reserved Instances and tried launching the RI but got stuck with a couple of things.

Please help me in clarifying:

  1. If I buy a reserved instance of 1 t2.large, can we run its equivalent t2. small or 8 t2.micro instance at the same cost (referring to its normalization factor in link above)?

  2. For this normalization on instance size flexibility to work, what offering class to be selected - "Standard" or "Convertible" or "Either should be fine"?

  3. Will the instance normalization work across different families of instances? i.e. m4.large with t2.medium?

  4. Will the instance normalization work across previous & current generation families? i.e. m4.large with m3.medium?

  5. We have 3 different AWS accounts with a consolidated billing, will this RI billings will be normalized across all 3 accounts?

  6. If I buy a RI of any class for 1 year and if I find that there is no such instance requirement in my account after 6 months, then still I need to pay the entire 1 year fees in monthly model (If I chose "No Upfront". The only way to get some money (if possible) would be to sell that in "Reserved Marketplace"?

  7. Do we have instance type flexibility only work with EC2 or for other resource types (RDS/Elasticache etc.)?

1
amazon-web-servicesamazon-ec2

1 Answers

5
votes

You've certainly done your research!

1. Normalization

Yes, 1 x t2.large (8GB RAM) = 8 x t2.micro (1GB RAM) = 4 x t2.small (2GB RAM).

2. Normalization class

Either Standard or Convertible works, but make sure it is a Regional RI (no AZ specified). If an AZ is specified, then it includes a capacity reservation but there is no normalization.

3 & 4. Normalization across families

No, RI benefits only work within the same family (eg m4).

5. Across consolidated accounts

RIs traditionally work across accounts linked by Consolidated Billing, so I would imagine that normalization would also work in this way. The benefit first goes to whichever account purchased the RI. Unused RIs in an hour then go to linked accounts.

6. Unwanted RIs

You are correct. If you purchase a monthly RI, you commit to pay the monthly fee for the entire period. The only way to stop this is to sell the RI on the Reserved Instance Marketplace.

Annual RIs are already fully-paid, but you can sell unwanted portions on the marketplace to earn some of your money back.

7. Instance Type flexibility for RDS, etc

Unsure, but I doubt that it would apply for other services unless specifically stated.