Specific Auto-Scaling group Cloudformation AWS

Question

I have an auto scaling group in AWS so i can change stack size of instances created by CF. However when i want to reduce the stack it will terminate random instances in the stack.

I need to know if its possible to reduce stack size in CF but leave specific instances in the stack running using the scaling group?

      "WebServerScaleUpPolicy" : {
  "Type" : "AWS::AutoScaling::ScalingPolicy",
  "Properties" : {
    "AdjustmentType" : "ChangeInCapacity",
    "AutoScalingGroupName" : { "Ref" : "AutoScalingServerGroup" },
    "Cooldown" : "60",
    "ScalingAdjustment" : "1"
  }
},
"WebServerScaleDownPolicy" : {
  "Type" : "AWS::AutoScaling::ScalingPolicy",
  "Properties" : {
    "AdjustmentType" : "ChangeInCapacity",
    "AutoScalingGroupName" : { "Ref" : "AutoScalingServerGroup" },
    "Cooldown" : "60",
    "ScalingAdjustment" : "-1"
  }
}

Any Help Appreciated.

Answer 1

Look into instance scale-in protection, as detailed in this AWS blog post.

I don't use CloudFormation so I'm not sure of the level of support it has for Autoscaling customisation, but this post has a workaround that may work for you.

Answer 2

Look into Amazon EC2 Auto Scaling Lifecycle Hooks . As you'll see below, instance can be notified of the Scale In event and either prepare for termination or straight up cancel the scaling event.