Types of Scaling

Manual scaling is the most basic way to scale your resources. Send an API call or use the Auto Scaling command line interface (CLI) to launch or terminate an Amazon EC2 instance. You need only specify the change in capacity you want. Auto Scaling manages the process of creating or destroying instances, including all the parameters to the Amazon EC2 runInstance call.

Sometimes you know exactly when you will need to increase or decrease the number of instances in your group, simply because that need arises on a predictable schedule. Scaling by schedule means that scaling actions are performed automatically as a function of time and date.

A more advanced way to scale your resources, scaling by policy, lets you define parameters that inform the Auto Scaling process. For example, you can create a policy that calls for enlarging your fleet whenever the average CPU utilization rate stays above ninety percent for fifteen minutes. This is useful when you can define how you want to scale in response to changing conditions, but you don’t know when those conditions will change. You can set up Auto Scaling to respond for you.

Note that you should have two policies, one for scaling up and one for scaling down, for each event that you want to monitor. For example, if you want to scale up when the network bandwidth reaches a certain level, you'll create a policy telling Auto Scaling to fire up a certain number of instances to help with your traffic. But you also want an accompanying policy to scale down by a certain number when the network bandwidth level goes back down.