Least Outstanding Requestsの注意点

AWSのALBでLeast Outstanding Requests（LOR）アルゴリズムを使う際の注意点をまとめたメモ。新しいターゲットがtarget groupに追加された直後は処理中リクエスト数が0のため、LORが集中的にリクエストを振り分けてしまう問題と、それを避けるためのオートスケーリング設定を引用している。2022年時点の情報。

Problems and solutions

Problem

The main risk when using the LOR algorithm is causing a flood of requests when a new target is added to the target group. In the LOR diagram above, Task 6 received 5 requests in quick succession, which might put it under high load.

Solution

The only way to avoid this issue is to ensure our autoscaling policy will launch at least a few tasks during each scale-up action.

Problem

The other potential issue is that a failing target will often respond quicker than a healthy one.

Solution

The other potential issue is that a failing target will often respond quicker than a healthy one.

References

• [AWS Application Load Balancer algorithms

  by Simon Tabor

  DAZN Engineering

  Medium](https://medium.com/dazn-tech/aws-application-load-balancer-algorithms-765be2eca158)