About zonal autoshift

Zonal autoshift is a capability where Amazon shifts application resource traffic away from an Availability Zone, on your behalf. Amazon starts an autoshift when internal telemetry indicates that there is an Availability Zone impairment that could potentially impact customers. The internal telemetry incorporates metrics from several sources, including the Amazon network, and the Amazon EC2 and Elastic Load Balancing services.

You must manually enable zonal autoshift for supported Amazon resources.

When you deploy and run Amazon applications on load balancers in multiple (typically three) AZs in a Region, and you pre-scale to support static stability, Amazon can quickly recover customer applications in an AZ by shifting traffic away with an autoshift. By shifting away resource traffic to other AZs in the Region, Amazon can reduce the duration and severity of potential impact caused by power outages, hardware or software issues in an AZ, or other impairments.

The resources supported by ARC provide integrations that mark the specified AZ as unhealthy, which results in traffic being shifted away from the impaired AZ.

When you enable zonal autoshift for a resource, you must also configure a practice run for the resource. Amazon performs practice runs about weekly, for 30 minutes, to help you make sure that you have enough capacity to run your application without one of the Availability Zones in the Region.

As with zonal shift, there are a few specific scenarios where zonal autoshift does not shift traffic away from the AZ. For example, if the load balancer target groups in the AZs don't have any instances, or if all of the instances are unhealthy, then the load balancer is in a fail open state and you can't shift away one of the AZs.

To learn more about zonal autoshift, see Zonal autoshift in ARC.