Auto Scaling group Availability Zone distribution - Amazon EC2 Auto Scaling
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Auto Scaling group Availability Zone distribution

The following information describes Auto Scaling group Availability Zone strategies.

Balanced best effort

Auto Scaling maintains an equal number of instances across enabled Availability Zones. If launch attempts fail in an Availability Zone, Auto Scaling attempts to launch instances in another healthy Availability Zone. This strategy is important for applications that need Availability Zone redundancy and are not impacted by imbalanced groups.

Balanced only

Auto Scaling maintains an equal number of instances across enabled Availability Zones. If launch attempts fail in an Availability Zone, Auto Scaling will continue to attempt to launch instances in the Availability Zone. This strategy is important to meet certain requirements such as quorum-based workloads or if your Auto Scaling group can tolerate the loss of an Availability Zone because you have sufficient capacity in the remaining Availability Zones.

The Availability Zone distribution strategy selection is in the Network section of the Amazon Web Services Management Console or you can use the create-auto-scaling-group or update-auto-scaling-group commands.

For more information, see Create Auto Scaling groups using launch templates.