When you set an RI Spend Coverage Target, you are defining how much of your EC2 spend you want ProsperOps to cover with RIs. Based on that target, ProsperOps automatically builds and manages an RI portfolio that optimizes your discount.
In most cases, execution of your portfolio will be immediate and your RI Spend Coverage will be just below your RI Spend Coverage Target. This is because ProsperOps has built an RI portfolio up to your defined target and purchasing any additional RIs would exceed that target.
In other cases, execution of your RI portfolio converges to the Spend Coverage Target over time or can drift from the target. Those reasons include:
- If you are at your RI Spend Coverage Target and your EC2 environment changes in a way that causes RIs to become unmatched, we will make sensible Convertible RI exchanges to ensure you continue receiving discounts from those RIs (if we didn't make exchanges, your savings would be impacted). We make efficient RI exchanges but AWS requirements dictate that every exchange results in a Spend Coverage increase. In dynamic environments, it's possible that this behavior could cause the Spend Coverage to creep above the Spend Coverage Target. ProsperOps favors maintaining or improving your discount over a strict adherence to the defined RI Spend Coverage Target.
- Certain EC2 instance usage is not consistent enough to warrant covering with RIs. When you set a Spend Coverage Target, we will build a portfolio up to that target, but will only do so when we determine an RI would actually generate savings. For example, if an instance is only run on weekends (2 days a week), purchasing an RI for it would increase your Spend Coverage but would result in negative savings. In those cases, we will defer purchasing RIs until we can safely determine that doing so would result in saving you money. Over time, if EC2 usage patterns shift, we will eventually build an RI portfolio up to the Spend Coverage Target.
- If ProsperOps hasn't yet purchased RIs up to the Spend Coverage Target, and EC2 spend declines below the Spend Coverage Target, we will cap RI purchases to 95% of EC2 spend. In other words, EC2 spend always takes precedence over RI Spend Coverage Target and ProsperOps will never make RI purchases that exceed your current EC2 spend.
- If you reduce your Spend Coverage Target or RI Portfolio Allocation in ways that can't be immediately implemented, your Spend Coverage will converge down to your Spend Coverage Target over time. Specifically, this will occur if you:
- Reduce your Spend Coverage Target below the Current Spend Coverage
- Decrease your 3 year RI Portfolio Allocation
- Decrease your 1 year RI Portfolio Allocation without also increasing your 3 year Portfolio Allocation by an equal or greater amount
In all cases above, there is nothing you need to do.