What routing method is used by the target group? (Not target group transfer from load balancer)

Question

I know that the target group routing method in the load balancer uses the round robin method.
https://docs.aws.amazon.com/ko_kr/elasticloadbalancing/latest/application/load-balancer-target-groups.html#modify-routing-algorithm

While using auto-scaling, I saw that multiple instances were attached to one target group, and I was curious about its routing method.

How do you route when multiple instances are attached to one target group?

Accepted Answer

Hi, its documented here.

Target group attributes

load_balancing.algorithm.type

The load balancing algorithm determines how the load balancer selects targets when routing requests. ( this applies to targets behind ASG as well )

The value is round_robin or least_outstanding_requests.

The default is round_robin.
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-target-groups.html

Answer

Like you mentioned, if multiple instances are attached to the same target group and the instances have a status of 'healthy' from the load balancer, the traffic will be evenly distributed in a round robin format to those instances. If you wanted the load balancer to route traffic in a different pattern to different target groups, you can configure that as well by using the "Weighted routing" option. Finally you can enable sticky sessions on you healthy instances within the target group for another routing option.

What routing method is used by the target group? (Not target group transfer from load balancer)

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