We created whichinstance.com a while ago to make it easier to decide which EC2 pricing option to use. Since then, we’ve gotten some questions on how to use it most effectively. To clarify its usage, I’ll walk through a couple of examples.
First generation Standard Medium instance, 100% utilization, 8 months
Hypothetical scenario: continuous integration box for a medium-term project (8 months). Since it’s a CI box for your hardworking global team, it needs to be running 24/7.
In the controls at the top, configure your desired region, and then select “Standard 1st gen” (since this is an m1 instance) and Medium. We’ll leave days at 365 since 8 months is close enough to the default.
8 months is about 244 days, and surprisingly enough the 3 year light utilization reserved instance turns out to be the cheapest.
However, 1 year light, 1 year medium, and 3 year light are all almost exactly the same cost. 1 year light is the cheapest before 8 months, while 1 year medium is the cheapest after 8 months. If it was up to me, I’d pick the 1 year medium in case an 8 month project becomes a 10 month project, but the cost of all 3 is fairly close. Then again, if it turns out to be a 14 month project, the 3 year light would be the best choice.
Second generation Standard XL instance, 60% utilization, 1.5 years
Hypothetical scenario: server used to run reports during business hours.
I’ve set up this graph at 730 days and 60% utilization, and the cursor highlight is at 1.5 years (548 days).
This time, with fractional utilization being taken into account, the heavy instances are nowhere near competitive price-wise, which makes sense. The 3 year light is the definite winner this time.
High CPU XL instance, 20% utilization, 2 months
Hypothetical scenario: short-term need for data processing once or twice a week.
An on demand instance is dramatically cheaper than the other options. Lest the previous two examples make it appear that reserved instances are the way to go, this should serve as a reminder that a lot of the value that EC2 offers is in cost-effectively handling occasional workloads.