How Auto Scaling Works

Eucalyptus Auto Scaling is designed to address a common web application scenario: that you are running multiple copies of an application across several identical instances to adequately handle a certain volume of user requests. Eucalyptus Auto Scaling can help you make more efficient use of the computing resources in your cloud by automatically launching and terminating these instances, based on metrics and/or a schedule that you can define. There are three main Auto Scaling components that work together to provide this functionality: the Auto Scaling group, the launch configuration, and the scaling plan.

The Auto Scaling group contains the information about the instances that will be actually be used for scaling operations. The Auto Scaling group defines the minimum, desired, and maximum number of instances that you will use to scale your application.

The launch configuration contains all of the information necessary for Auto Scaling to launch instances, including instance type, image ID, key pairs, security groups, and block device mappings.

The scaling policy defines how to perform scaling actions. Scaling policies can execute automatically in response to CloudWatch alarms, or they you can execute them manually.

In addition to performing scaling operations based on the criteria defined in the scaling plan, Auto Scaling will periodically perform health checks to ensure that the instances in your Auto Scaling group are up and running. If an instance is determined to be unhealthy, Auto Scaling will terminate that instance and launch a new instance in order to maintain the minimum or desired number of instances in the scaling group.