Reserved Instances

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What if I have 1 RDS instance A that runs 24 hours a day and I also have 2 instances (B and C) that run concurrently between 7AM and 7PM (they are stopped at night). If I purchase 2 Reserved Instances would that be enough to cover the full usage of my 3 instances A, B and C? I know that if B and C ran consecutively it would be, but what hapens when they run concurently? Their usage adds up to 24 hour per day, but is that how the RI can be applied? I am assuming all the instances are in the same region and are the same instance type and size.

  • Can someone answer this query on priority?

    Thanks in advance..

demandé il y a un an375 vues
3 réponses
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Customers using both Reserved and On-Demand instances will have Reserved Instance rates applied first to minimize costs. You pay the low hourly usage fee for every hour in your Reserved Instance term (which means you’re charged the hourly fee regardless of whether any usage has occurred during an hour). When your total quantity of running instances during a given hour exceeds the number of applicable Reserved Instances you own, you will be charged the On-Demand rate.

For example, if you own three Reserved Instances with the same instance attributes and region (or Availability Zone if applicable), the billing system checks each hour to see how many total instances you have running that match those parameters. If it is three or less, you will be charged the Reserved Instance rate for each matching instance running that hour. If more than three are running, you will be charged the On-Demand rate for the additional instances.

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

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kentrad
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Chris_G
vérifié il y a un an
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No, in your scenario you cannot purchase 2 RIs and hope to cover all the instances that are running concurently.

The billing works hourly. It means that every hour the system wll be checking how many running instances you have and how many RIs are there to cover them (this works the same for RDS as for EC2, as for any other RIs for other services... like ElastiCache, etc...)

In your example... if you purchase 2 RIs, then your first RI will be 100% utilized by your RDS instance that is running 24/7. Your second RI will be only utilized 50% of the time (assuming that you have 2 instances running for 12 hours of the day, and they are not running for the remaining hours), and the second running RDS instance will be charged on-demand rate.

For the remaining 12 hours when those 2 instances are not running, your second RI will not be utilized at all. And thus, you will be losing on the $ discount during those hours (that discount cannot be reused at a later time).

So, be considerate of your usage - to avail of RDS RIs you need to have consistent HOURLY usage throughout the term of your commitment.

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répondu il y a un an
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As per the other answer, instances that are running concurrently aren't counted as running consecutively. Instead you might consider Savings Plans.

Edit: Of course, Savings Plans are not available for RDS; this would only apply to EC2.

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