Fast Launch automatically launch instances for ACG


Why does enabling fast launch for windows on an AMI connected to an automatic scaling group launch EC2 instances not initiated by the ASG?

It seems in the EC2 list that instances are popping up as soon as I enable the fast launch, but the ASG group is not in an alarm start or have scale-in actions

  • Can you check the Tags on one of the new instances to confirm its being launched by the AutoScaling Group? If yes, can you check the "Activity" tab of the Group and see what reason it gives for launching the new instances?

  • It's not started by the ASG. It seems it might be part of the provisioning of the Fast Launch that it starts EC2 instances. But the Fast Launch enabling always fails with the reasoning: Unable to stop instance (ID=i-xx) for snapshot creation.

asked 4 months ago214 views
1 Answer

The Fast Launch feature itself launches temporary instances, which are used to do the prep steps which happen on the first Windows boot. See the steps at the top of this doc for more details:

If you're using an ASG, then you could instead use a Warm Pool, which accomplishes a similar goal. It allows you to pre-provision instances, take care of the delays from the first Windows boot, as well as run any user-data you might want to get your application setup. After that's all done, you would complete the Lifecycle Hook on the ASG (as the last step in the userdata script), which tells the ASG to Stop that instance until its needed for a scale-out action

answered 4 months ago

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