Considering upgrading your EC2 r3 to r4 instances? Beware if you are running Windows!

I could not believe my eyes when I did what I thought was a no-brainer earlier this year: compare the instance pricing for AWS’ latest memory-optimized instance. Here is what I found:

While both OnDemand and RI pricing (1yr, partial upfront) is 11–20% cheaper for Linux, the r4 instances it can be much more expensive when looking at Windows OnDemand and RI cost for the same terms. For the larger r4.8xlarge instances the RI (1yr, partial upfront) price tag is actually 62% more expensive!

Figure 1: EC2 r4 instance pricing compared to r3 instance pricing

Figure 2: EC2 r4.large to r4.8xlarge instance pricing deltas

So if you are running r3.4xlarge or r3.8xlarge RIs on Windows, you may want to think twice before jumping onto the latest instance class.

I am actually running countless r3.8xlarge 1yr partial upfront Windows RIs and overseeing this little detail could have cost us close to half a million dollars in a year. I am really glad I did my due diligence, analyzed the instance pricing properly and not let myself fool by just looking at the better specs.

My advice: don’t take changing instance types lightly, especially when you support large workloads and deal with hundreds of instances.