We are doing some preparation for moving from Intel-based architecture to ARM-based CPUs. As part of this testing we’ve set up a parallel stack on a different queue to run our CI on ARM. The stack spins up instances and runs tests for the right queue as expected. Unfortunately we’re seeing an issue …

Hey @geoffharcourt , Thanks for getting in touch – it sounds like you have disable_scale_in set to true in this case. If that’s correct, we’d recommend setting this to false to ensure that the scale is able to reduce the desired capacity. Would you be able to share the parameters of your Stack for …

Hi Joe, Thanks for responding! I forwarded our stack parameters to support@buildkite.com . I can set disable_scale_in to false, but our Intel stack has it as true and seems to scale down so I’m confused as to what’s making the idle termination behavior different on the two stacks.

Hey @geoffharcourt , We’ve observed that the disable_scale_in setting (which is exposed by NewInstancesProtectedFromScaleIn as a parameter) was preventing instances from being scaled-in by our Agent Scaler, which would result in Agents hanging. The ASG itself would be prevented from terminating the…

We figured out what was going on. We were re-using the instance role from two stacks and the instance role’s InstancePolicy inline policy didn’t have auto-scaling group instance termination privileges and was therefore unable to scale in on the stack. We’ve fixed that permission on our instance role…

ARM stack does not seem to scale down

Elastic CI Stack for AWS

geoffharcourt December 3, 2025, 4:14pm 4

I’m also wondering if this behavior Max describes is the same thing I’ve been seeing: Experimental Lambda-based Scaler 🦑 - #14 by max

Topic		Replies	Views
Experimental Lambda-based Scaler 🦑 Elastic CI Stack for AWS	14	4865	September 25, 2024
Idle Buildkite Agent is trying to terminate instance Elastic CI Stack for AWS	2	384	September 7, 2023
Autoscaling disconnects active agents Elastic CI Stack for AWS	11	491	August 1, 2023
AWS Stack upgrade from v5.21.0 to v6.4.0 Elastic CI Stack for AWS	4	478	September 4, 2023
Buildkite Elastic CI Stack for AWS v5.0.0 released Announcements	1	1578	November 9, 2020

ARM stack does not seem to scale down

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