Auto Scaling Policies

The new release of Auto Scaling gives you better control over the policies used to modify the number of EC2 instances running in one of your AutoScaling groups.

Auto Scaling now emits metrics for each AutoScalingGroup. You can use CloudWatch to monitor your group size, instances being launched and terminated, and other group activity.

Policies are used to compute the group’s new capacity using a combination of a type and a scaling Increment. The type controls whether the increment is interpreted as an absolute value or as a percentage.

Here are some examples:

• Type is PercentOfCapacity and Increment is 100: The group will double in size when the policy is executed.
• Type is PercentOfCapacity and Increment is -50. The group size will be halved when the policy is executed.
• Type is Absolute and Increment is 1. One instance will be added to the group when the policy is executed.
• Type is Absolute and Increment is -2. Two instances will be removed from the group when the policy is executed.

You can now attach up to 25 policies to an AutoScaling group, and you can use the new ExecuteAction function to scale a group using the policy of your choice.

— Jeff;