Description

This policy checks that AWS EC2 Auto Scaling Groups that use a mixed instances launch template but do not have Capacity Rebalancing enabled.

Capacity Rebalancing helps you maintain application availability by proactively launching a new Spot Instance to replace one that is at an increased risk of interruption.

Rationale

Spot Instances offer a cost-effective way to run workloads, however, they can be interrupted when EC2 reclaims capacity. Enabling Capacity Rebalancing helps minimize the impact of such interruptions. When a Spot Instance receives a rebalance recommendation, the Auto Scaling group proactively launches a replacement instance, allowing your application to maintain stability and performance before the original instance is terminated.

Impact

If Capacity Rebalancing is not enabled, your application may experience reduced availability or performance degradation when Spot Instances are interrupted and replacements cannot be provisioned promptly.

Audit

This policy flags an AWS EC2 Auto Scaling Group as INCOMPLIANT if if it uses a mixed instances launch template and Capacity Rebalancing is not set to Enable.

The ASG is marked as INAPPLICABLE if the Mixed Instances Launch Template ID is empty.