If RIs for your RDS instance are “Size Flexible”, you can and should take action before resolving rightsizing uncertainties. This article gives context on what this means and how it allows you to flexibly cover a portion of your RDS instance spend.
We consistently see companies paralyzed from acting on RDS commitments because they don’t want to get commitments on inefficient resource usage. Very fair concern, but there’s impactful waste incurred every day this paralysis continues.
The cycle goes something like this:
If RIs for your RDS instance are “Size Flexible”, you can and should take action before resolving rightsizing uncertainties. This article gives context on what this means and how it allows you to flexibly cover a portion of your RDS instance spend.
As of this article’s writing, RDS Instances with the following DB engine and license model:
To quote the RDS faq : It means the reservation will “automatically apply to a running DB instance of any size within the same instance family (e.g. M4, T2, or R3) for the same database engine and Region. In addition, the reservation will also apply to DB instances running in either Single-AZ or Multi-AZ deployment options.For example, let’s say you purchased a db.m4.2xlarge MySQL reservation. If you decide to scale up the running DB instance to a db.m4.4xlarge, the discounted rate of this RI will cover 1/2 of the usage of the larger DB instance.”
For AWS’ detailed description, see How Reserved Instances are applied here.
The key metric that determines how the size flexible reserved instance is applied is the “normalization factor”. A snippet of the normalization factor table and AWS’ example graphics below.
In the reservation, check for “Size Flexible: Yes”. See screenshot below.
Quick wins. Potential no-risk savings.
If you’re using native tools, this means digging into Cloudwatch usage data to evaluate overprovisioned resources.
If you’re using Cloudthread, you can see all RDS rightsizing opportunities from across regions/accounts in your Opportunities Explorer.
If it’s an instance you’ll use for the coming year, it’s worth covering with an RI to realize zero-engineering-effort savings.
This will be unique to your infrastructure requirements and bandwidth.
If you do rightsize the instance, great, you’re already covered by the appropriate RI and you’ve been saving since the moment you bought it. If you don’t rightsize the instance, given the nature of size flexible reservations, you can purchase an additional reservation to achieve full coverage.
