aws reserved instance allocation with multiple linked accounts

Question

We have a situation where a client has multiple AWS linked accounts as part of a Master acct. Each linked account has resources in many regions/Availability zones.

Client wants to buy RI's and allocate them to various customers to increase margin.

Questions:

*Can we purchase RI's at a sub account level or Master only? *If we can purchase at a sub account level then will those be applied to the PayGo instances *in that sub account only ? *Is there any control we can exercise or algorithms we can enable to funnel this logic? *If the utilization of the RI decreases and the utilization within another PayGo VM increases will the RI be automatically applied to this new instance ?

Thanks

Answer 1

From Amazon documentation:

Note

When AWS assigns Reserved Instance hours to linked accounts, it always starts first with the linked account that purchased the reservation, which is sometimes called Reserved Instance affinity. If there are hours from the capacity reservation left over, they are applied to other accounts operating identical usage types in the same Availability Zone. Again, this allocation always occurs using unblended rates.

This means that the account from which the reservation was made gets to utilize reserved hours first, and any left-overs will be utilized by other accounts in the family according to usage type and availability zone.

Answer 2

It doesn't matter in which account you purchase RIs, but if those are convertible RIs and you are planning to exchange those regularly (to meet compute usage changes) then you should stick to using one account only for all RIs.