Improving availability with Application Load Balancer automatic target weights

This article introduces the Application Load Balancer Automatic Target Weights (ATW) feature, which helps reduce errors for web application users by detecting and mitigating gray failures in targets behind an Application Load Balancer (ALB).

Specifically, the article covers:

• Anomaly detection: ATW analyzes HTTP status codes and TCP/TLS errors to identify targets with a disproportionate ratio of errors compared to other targets in the same target group.
• Anomaly mitigation: When anomalous targets are detected, ATW reduces traffic to the under-performing targets and sends more traffic to healthy targets. When the errors decrease, traffic is gradually increased to the recovered targets.
• Viewing effectiveness: CloudWatch dashboards can be used to monitor the impact of ATW anomaly detection and mitigation on HTTP errors and successful responses.
• Considerations: Important points to keep in mind when using ATW, such as minimum number of targets, cross-zone behavior, request rate requirements, and limitations.
• Conclusion: ATW is now available in all commercial AWS Regions and can be enabled on existing and new ALBs to improve application availability.