I'm considering purchasing an Amazon AWS EC2 reserved instance. Does any one know of any performance benefits for reserved vs. on-demand, spot instances? Or is this simply a pricing difference? Do reserved instances get spun up on VMs with less congestion and that sort of thing is what I'm thinking about.
Thanks, Michael
Despite its name, "reserved instance" is a billing construct, not an instance type. When you purchase a reserved instance, no instance is started. It simply affects the price you pay for a standard on-demand instance that matches the availability zone, instance type, operating system of the reserved instance purchase.
Purchasing a reserved instance can reduce the hourly price you pay for an on-demand instance that has already been running for months. If you terminate that on-demand instance, the reserved instance pricing switches to any other on-demand instance that is running and matches the specs.
Spot instances are the same as on-demand instances except in when they are started/terminated and how much they cost.
Spot instances are basically when amazon has unused resources they can sell them at a slightly lower price to hopefully get those used up. The issue with spot instances is that they can be shut off at any time so you're taking a risk.
Reserved instances are computing power you can purchase upfront at a discounted rate. You're basically saying that you're going to use this type of system for 1 or 3 years or if you're not going to use it you want to ensure that you can use it at any time.
On-demand is the default for most people, I think. They're there. They're available when you need them and when you don't need them you stop paying for them.
If you purchase the same types of machine configs for each type of instance then there is no performance difference, only price.
Adding to what @BuildStarted said, I have noticed longer start times with spot instances. I'm guessing that's because there is some additional time needed to compute the current spot price and find capacity.
Once an instance is up and running, though, you shouldn't see any difference between the 3 pricing methods for the same instance type.
