Posted On: Nov 25, 2019

Least outstanding requests (LOR) algorithm is now available for Application Load Balancer. This is in addition to the round-robin algorithm that the Application Load Balancer already supports. Customers have the flexibility to choose either algorithm depending on their workload needs. 

Prior to this announcement, Application Load Balancer exclusively used a round-robin algorithm to distribute incoming requests to backend targets. The requests would be distributed among all the targets of a target group in a round-robin fashion without consideration for capacity or utilization. This led to over-utilization or under-utilization of targets in target groups when requests had varied processing times or targets were frequently added or removed.  

Starting today, customers can opt to use the LOR algorithm to route requests within a target group. With this algorithm, as the new request comes in, the load balancer will send it to the target with least number of outstanding requests. Targets processing long-standing requests or having lower processing capabilities are not burdened with more requests and the load is evenly spread across targets. This also helps the new targets to effectively take load off of overloaded targets. 

LOR algorithm is available today for all existing and new Application Load Balancers in all regions. You can choose the algorithm at target group level using the AWS Management Console, AWS Command Line Interface (CLI), and AWS SDKs.

Learn more about when and how to use the LOR algorithm on Application Load Balancer here.