What is the behavior of "WillReplace" in CloudFormation?

Question

In CloudFormation, you can set WillReplace for an update policy.

UpdatePolicy:
  AutoScalingReplacingUpdate:
    WillReplace: Boolean

Does it refer to replacing the Autoscaling group with a new one, or replacing the instances in the Auto scaling group?

Answer 1

AWS docs write that it replaces ASG itself. This means, instances will be also replaced:

Specifies whether an Auto Scaling group and the instances it contains are replaced during an update.