Have you heard people talking about purchasing Reserved Instances (RIs) but you don't know where to start? Maybe you've been purchasing RIs but don't have a good way of checking their utilisation. Maybe you're somewhere in between and you need help to figure out where to focus your efforts. 

The Reservations page in Stax Spotlight helps you get a better understanding of Reserved Instances and how they can help save you money. 

How do I use the Reservations page?

View the percentage of your EC2 spend that is covered by RIs. 

This looks at your total EC2 On Demand spend, and shows you how much of that is covered by RI purchases you've already made.
Because purchasing Reserved Instances in advance often comes with a substantial discount, they can save you a lot of money. 

There's no 'magic number', but it's generally safe to plan on at least 30% coverage. This should be on servers that run 24/7. If you purchase too many RIs, you're going to be wasting any hours that go unused. It's a balancing act, but there are generally safe ways of going about it.

Where to focus your efforts

Here we look at what percent of the instance type is currently covered by RIs, and how expensive the instance type is, so you can focus on where you'll make the most impact in reducing AWS spend.
Start with the biggest red dot to get the biggest saving, and work your way down.

Which RIs to purchase to reduce your AWS cost

Want more details to help you make your RI decisions? Click on the instance type and we'll give you more detailed data on what you can expect to save with the purchase we've recommended. 

We make our calculations based on 1 year no upfront cost RIs, because that's the most conservative option. If you choose a longer period or more upfront, you just save more! 

We also only look at your On Demand EC2 spend, as it doesn't make sense to look at Spot Instances.

Things to keep in mind before taking the RI plunge

Only buy reservations for those apps where:

  • Your cost baseline is clean.
  • Your architecture won't change in the next 6-9 months.
  • They cost a significant amount of money.

When buying RIs:

  • Always choose a 1 year term.
  • Always buy standard, not convertible RIs.
  • Don't specify an availability zone.

This gives you the best balance of discounts vs flexibility.

When you're purchasing RIs, you're going to be getting a discount for committing upfront, but be sure that you weigh these factors in before making your decision:

  • You can be penalised if you change your instance type down the track, so make sure that you're confident that your spend for that instance type will either stay the same or increase for the period for which you're purchasing. This also applies if an instance type gets updated.
  • If you know your infrastructure is going to change significantly, it's probably not a good time to buy. Wait until things settle down and you have some predictability.
  • AWS prices tend to reduce over time. When you buy an RI, you're locking that price in, so you won't be able to take advantage of any price drops.
  • Our recommendations are just that. We only look at your an account from an API level. You know your infrastructure better than we ever could, so please ensure that you do a sanity check on our recommendations before taking action.
  • It's worth noting that there's generally no particular individual instance "covered" by RIs as far as EC2 is concerned, it's on an hour by hour basis. 
  • AWS allows "instance size flexibility" for Linux instances. This means that a smaller size will "flex" up to cover parts of a bigger instance. Conversely, a bigger size will flex down to cover smaller sizes.

Not seeing these recommendations? If you're not using the most up-to-date version of our IAM role, you'll need to update it to be able to see our recommendations. Check out this article to find out how to update your roles.

As always, if you have any questions about Stax or any requests, please email us at support@stax.io

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