Aregional managed instance group (MIG)is not balanced if the difference in the number of VMs betweentwo zones is 2 or more VMs. A regional MIG can fall out of balance if youdisableproactive instance redistributionand then delete or abandon instances to cause an uneven distribution acrosszones.

If your group is not balanced and you want to re-enable proactive instancedistribution, you must first manually rebalance your group to achieve an evendistribution of instances across zones.

Manually rebalance by deleting VMs or resizing the group

You can manually rebalance your group to achieve an even distribution ofinstances across zones bydeletingVMs from zones with more instances or byresizingto add instances to zones with fewer VMs until the distribution is even.

When you resize a MIG that has proactive instance redistribution turned off,the group stillopportunistically converges toward balance, treating eachresize operation as an opportunity to balance the group:

• When the group grows, the group always tries to add VMs to the zones withthe smallest number of VMs.
• When the group shrinks, the group always removes VMs from the zones with thelargest number of VMs.

What's next

• Learn how to re-enable or disableproactive redistribution.
• Learn how to set a regional MIG'starget distribution shape.