Cost of Reserved Instances when the AZ fails

Question

Suppose I buy Zonal Reserved Instance (in a specific AZ) to ensure Capacity Reservation (which is important to us), what will happen to Reserved Instance discount if that whole AZ fails? AWS will allow us to launch the instance in other AZs but will the discount apply for the new AZ? given that this was AZ switchover forced by the AWS infrastructure.

Riku_Kobayashi · Answer

The following document states that payment is made regardless of actual use, so it may be that AZ failure will also result in payment.  
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/concepts-reserved-instances-application.html
> All Reserved Instances provide you with a discount compared to On-Demand pricing. With Reserved Instances, you pay for the entire term regardless of actual use. You can choose to pay for your Reserved Instance upfront, partially upfront, or monthly, depending on the payment option specified for the Reserved Instance.

I think you should open a case with AWS support with "Account and billing" to be sure.

hayao-k · Answer

Unfortunately, the discount is not applied in different AZs in case of AZ failure for Zonal Reserved Instances.  
Savings Plans do not have capacity reservations, but they can be used with on-demand capacity reservations, which may be more suitable in your case.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/capacity-reservations-pricing-billing.html#capacity-reservations-pricing  
> Billing discounts for Savings Plans and Regional Reserved Instances apply to Capacity Reservations. For more information, see Billing discounts.

Cost of Reserved Instances when the AZ fails

Relevant content