Handing the replacement loop to the Instance Refresh engine means CloudFormation stops owning a job it used to do badly. The teardown's phrasing is that CloudFormation becomes an intent orchestrator rather than a replacement executor [8]. That is the right split. It also means every failure mode of Instance Refresh is now a failure mode of a stack update, and stack updates are what change management watches.
Start with capacity. Launch-Before-Terminate validates new instances as InService in the target group before terminating the old ones [9], with the ELB health check acting as the in-service gate [16]. Headroom is configured through MinHealthyPercentage and MaxHealthyPercentage, and the post puts the typical figure at 10% to 100% above DesiredCapacity [10]. At those bounds, peak running count during a refresh sits between 1.1x and 2x DesiredCapacity [17]. On an r6i.8xlarge fleet that is not a rounding error, which is why the post tells you to plan for it [11]. The corollary is less obvious: anything that keeps a new instance out of the target group keeps the refresh from progressing, so your health check definition is now part of your deploy timeout budget.
Bake time is the other axis. Checkpoints are progress percentages with a BakeTimeSeconds attached, 20/50/100 in the post's example [13], and during each pause the engine evaluates CloudWatch alarms wired as abort conditions [14]. Three checkpoints therefore add at least three bake windows of deliberate waiting to one stack update, before counting replacement time [18]. The gate is only as good as the alarm behind it. If the alarm needs more data points than the bake window supplies, the checkpoint passes on ignorance and you have bought latency without buying safety.
The rollback path is cleaner than what it replaces, and incomplete in the write-up. An alarm in ALARM state aborts the refresh, and CloudFormation initiates a stack rollback that restores the previous Launch Template as declared state [15]. Under AutoScalingRollingUpdate, a stack rollback left already-replaced instances alone [5]; under out-of-band refresh, rollback was manual and untraceable in change management [6]. What the teardown does not say is what happens to instances already carrying the bad AMI once the previous template is restored. Restoring a template is itself a property change [7]. Whether that triggers a second refresh, and how the abort alarm behaves during it, is what I would exercise in a staging ASG before trusting this in production.
One note on provenance. This is a single dev.to pattern teardown, which dates the native policy to July 2026 and ReplaceRootVolume to November 2025 [2][12], and frames the drift problem through PCI-DSS and SOC 2 in a financial-sector example [4]. The compliance argument transfers only if your auditors read stack state as evidence of instance state, while the mechanism holds either way.
