Batch size on AutoOSUpgrade

Batch size on AutoOSUpgrade

Author: mayanknayar

articles/virtual-machine-scale-sets/virtual-machine-scale-sets-automatic-upgrade.md

@@ -30,7 +30,7 @@ An upgrade works by replacing the OS disk of a VM with a new disk created using
 
 The upgrade process works as follows:
 1. Before beginning the upgrade process, the orchestrator will ensure that no more than 20% of instances in the entire scale set are unhealthy (for any reason).
-2. The upgrade orchestrator identifies the batch of VM instances to upgrade, with any one batch having a maximum of 20% of the total instance count. For smaller scale sets with 5 or fewer instances, the batch size for an upgrade is one virtual machine instance.
+2. The upgrade orchestrator identifies the batch of VM instances to upgrade, with any one batch having a maximum of 20% of the total instance count, subject to a minimum batch size of one virtual machine.
 3. The OS disk of the selected batch of VM instances is replaced with a new OS disk created from the latest image. All specified extensions and configurations in the scale set model are applied to the upgraded instance.
 4. For scale sets with configured application health probes or Application Health extension, the upgrade waits up to 5 minutes for the instance to become healthy, before moving on to upgrade the next batch. If an instance does not recover its health in 5 minutes after an upgrade, then by default the previous OS disk for the instance is restored.
 5. The upgrade orchestrator also tracks the percentage of instances that become unhealthy post an upgrade. The upgrade will stop if more than 20% of upgraded instances become unhealthy during the upgrade process.