Saving plan and RI purchase.

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Hello Team, I have two C5a.xlarge windows instance running for 16 hours per day simultaneously. I want to purchase RI/SP to lower down my EC2 bill.

As per the Calculation: Number of Total Usage Hours : 16hours/day X 30 Days X 2 Vm = 960 Hours.
The On-demand price for both Ec2 will be near around : Approx USD 268 Monthly

I need to know if i purchase a single RI , then it will be applicable to both the instance or i need to purchase two different RI.

Also If i purchase a single Saving plan then what will be the per hour commitment i should put and what will be the cost saving

2 Answers
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Hello,

please try this solution it will be helpful for you.

To reduce your EC2 costs for two C5a.xlarge Windows instances running 16 hours per day, you should consider purchasing either Reserved Instances (RI) or a Savings Plan (SP). Since RIs are applied individually, you would need to purchase two RIs to cover both instances. Alternatively, with a Savings Plan, you can commit to a discounted rate based on your hourly usage. For your usage of 960 hours per month, the SP would require an hourly commitment of approximately USD 0.279. Generally, a Savings Plan offers more flexibility and potential savings compared to RIs, making it a better choice if your usage patterns might change.

please look at AWS Document link you will get more information.

https://docs.aws.amazon.com/savingsplans/latest/userguide/sp-applying.html

https://aws.amazon.com/ec2/pricing/reserved-instances/pricing/

answered 16 days ago
  • My single VM on demand cost will be USD 135/ Month. And as per the below calculation. the $/Hour commitment comes out to be 0.187903 . If i put this commitment while purchasing SP, then is this cover my both Instances usage.,

    As single instance run for 16 hours. So total woking hour will be 32 hours. Did this SP cover 24 hours out of it and rest is OD.

    And also How USD 0.279 value arrive. If this is the committment then it hardly save any cost as the OD cost will be 270 usd per month for both instance and with 0.279 it will be 267 Usd.

    Type C5a.xlarge Hours/Month 480 $/Month 135.29 $/Day 4.509667 $/Hour 0.187903

  • The Savings Plans rate (one-year with no Upfront) for c5a.xlarge for Windows in US-EAST-1 is $0.296. For two c5a.xlarge, your hourly commitment would be $0.296 x 2 = $0.592. Monthly commitment would be $0.592 x 24 x 30 = $426.24. If you run both them for 24 hours a day, the OnDemand cost would be $0.338 x2 x 24 x 30 = $486.72 which is about 12% savings. But if you only run them for16 hours a day, you are not saving. That's because the instances are only running 16/24 = 67% and c5a.xlarge only offers 12% savings ($0.296 / 0.338 = 88%).

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Understanding RIs and Savings Plans Reserved Instances (RI):

  • RIs are applied to a specific instance type, region, and other parameters.
  • Each RI applies to one instance, meaning if you have two instances running simultaneously, you need two RIs to cover both.
  • RIs provide a discount on the hourly rate in exchange for a one- or three-year commitment. Savings Plans:

Savings Plans are more flexible compared to RIs.

  • They provide a discount on any usage within a specified region.
  • You commit to a certain amount of usage (e.g., $/hour) over a one- or three-year term.
  • The plan automatically applies the discount to your usage regardless of instance type, making it more versatile. For details about pricing Go through linls:

Calculate your potential savings for both RIs and SPs using the AWS pricing calculator

https://aws.amazon.com/savingsplans/

https://aws.amazon.com/ec2/pricing/reserved-instances/pricing/

answered 16 days ago
  • Is a single saving plan with the commitment of 0.187 USD work here, does it cover my both instances... Also want to know that if my both Ec2 run for 16 hours each i,e 32 hours in a day. whether it will cover 24 hours as in SP and remaining in OD ?

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