Читать книгу AWS Certified Solutions Architect Study Guide - Ben Piper, David Higby Clinton - Страница 82

An Auto Scaling group is a group of EC2 instances that Auto Scaling manages. When creating an Auto Scaling group, you must first specify either the launch configuration or launch template you created. When you create an Auto Scaling group, you must specify how many running instances you want Auto Scaling to provision and maintain using the launch configuration or template you created. You must specify the minimum and maximum size of the Auto Scaling group. You may also optionally set the desired number of instances you want Auto Scaling to provision and maintain.

 Minimum Auto Scaling will ensure the number of healthy instances never goes below the minimum. If you set this to 0, Auto Scaling will not spawn any instances and will terminate any running instances in the group.

 Maximum Auto Scaling will make sure the number of healthy instances never exceeds this amount. This might seem strange but remember that you might have budget limitations and need to be protected from unexpected (and unaffordable) usage demands.

 Desired Capacity The desired capacity is an optional setting that must lie within the minimum and maximum values. If you don't specify a desired capacity, Auto Scaling will launch the number of instances as the minimum value. If you specify a desired capacity, Auto Scaling will add or terminate instances to stay at the desired capacity. For example, if you set the minimum to 1, the maximum to 10, and the desired capacity to 4, then Auto Scaling will create four instances. If one of those instances gets terminated—for example, because of human action or a host crash—Auto Scaling will replace it to maintain the desired capacity setting of 4. In the web console, desired capacity is also called the group size.