When you setup an Auto Scaling groups in AWS EC2 Min and Max bounds seem to make sense:
- The minimum number of instances to scale down to based on policies
- The maximum number of instances to scale up to based on policies
However, I've never been able to wrap my head around what the heck Desired is intended to affect.
I've always just set Desired equal to Min, because generally, I want to pay Amazon the minimum tithe possible, and unless you need an instance to handle load it should be at the Min number of instances.
I know if you use ElasticBeanstalk and set a Min to 1 and Max to 2 it sets a Desired to 2 (of course!)--you can't choose a value for Desired.
What would be the use case for a different Desired number of instances and how does it differ? When you expect AWS to scale lower than your Desired if desired is larger than Min?