Posted On: Feb 22, 2018

Network Load Balancer can now distribute requests regardless of Availability Zone with the support of cross-zone load balancing. This feature allows Network Load Balancer to route incoming requests to applications that are deployed across multiple Availability Zones.

Network Load Balancer relies on Domain Name System (DNS) to distribute requests from clients to the Load Balancer nodes deployed in multiple Availability Zones. Prior to this support, Network Load Balancer routed requests only to targets located in the same Availability Zone. This meant that in scenarios where the clients were caching the DNS information of a zonal Network Load Balancer, some targets could receive a disproportionally higher number of inbound requests. 

In addition, if you did not have an equal number of healthy targets in each of the Availability Zones (e.g. if you had taken some targets down for maintenance), your requests would be balanced across a smaller number of healthy targets in the affected Availability Zones - meaning that you would have to closely monitor and adjust your target capacity. 

If you enable cross-zone load balancing, you no longer have to worry that clients caching DNS information will result in requests being distributed unevenly. With this launch, requests are distributed equally to your targets regardless of the Availability Zone in which they are located. This feature makes it easier for you to deploy and manage your applications across multiple Availability Zones. When you enable cross-zone load balancing for your Network Load Balancer, regional data charges apply.  

To learn more about cross-zone load balancing, please visit the Network Load Balancer Guide