Zonal shift for your Network Load Balancer
Zonal shift is a capability in Amazon Application Recovery Controller (ARC). With zonal shift, you can shift a Network Load Balancer resource away from an impaired Availability Zone with a single action. This way, you can continue operating from other healthy Availability Zones in an AWS Region.
When you start a zonal shift, your Network Load Balancer stops sending traffic for the resource to the affected Availability Zone. However, it can take a short time, typically up to a few minutes, to complete existing, in-progress connections in the affected Availability Zone for Network Load Balancers with cross-zone load balancing disabled. Zonal shift does not support terminating in-progress connections on Network Load Balancers with cross-zone load balancing enabled. For more information, see How a zonal shift works: health checks and zonal IP addresses in the Amazon Application Recovery Controller (ARC) Developer Guide.
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Before you begin a zonal shift on your Network Load Balancer
Before you begin using zonal shift on your Network Load Balancer, be aware of the following:
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Zonal shift is disabled by default and must be enabled on each Network Load Balancer. For more information, see Enable zonal shift for your Network Load Balancer.
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Zonal shift isn't supported when you use an Application Load Balancer as an accelerator endpoint in AWS Global Accelerator.
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You can start a zonal shift for a specific Network Load Balancer only for a single Availability Zone. You can't start a zonal shift for multiple Availability Zones.
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AWS proactively removes zonal Network Load Balancer IP addresses from DNS when multiple infrastructure issues impact services. Always check current Availability Zone capacity before you start a zonal shift. If you use a zonal shift on your Network Load Balancer, the Availability Zone affected by the zonal shift also loses target capacity.
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During zonal shift on Network Load Balancers with cross-zone load balancing enabled, the zonal load balancer IP addresses are removed from DNS. Existing connections to targets in the impaired Availability Zone persist until they organically close, while new connections are no longer routed to targets in the impaired Availability Zone.
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When an Application Load Balancer is a target of a Network Load Balancer, always start the zonal shift from the Network Load Balancer. If you start a zonal shift from the Application Load Balancer, the Network Load Balancer doesn't recognize the shift and continues to send traffic to the Application Load Balancer.
For more information, see Best practices with Route 53 ARC zonal shifts in the Amazon Application Recovery Controller (ARC) Developer Guide.
Zonal shift administrative override
Targets that belong to a Network Load Balancer will include a new status AdministrativeOverride, which is independent from the
TargetHealth state.
When a zonal shift is started for a Network Load Balancer, all targets within the zone being shifted away from are considered administratively overridden. The Network Load Balancer will stop routing new traffic to the administratively overridden targets, however existing connections remain intact until they are organically closed.
The possible AdministrativeOverride states are:
- unknown
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State cannot be propagated due to an internal error
- no_override
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No override is currently active on target
- zonal_shift_active
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Zonal shift is active in target Availability Zone
- zonal_shift_delegated_to_dns
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This target's zonal shift state is not available through DescribeTargetHealth but can be viewed directly through the Amazon ARC API or console
