Ensure there are at least two healthy EC2 target instances registered to each Amazon Application Load Balancer (ALB) and Network Load Balancer (NLB) in order to provide a fault-tolerant load balancing configuration for your applications.
This rule can help you work with the AWS Well-Architected Framework
This rule resolution is part of the Cloud Conformity Security & Compliance tool for AWS
To achieve fault tolerance and minimize the risk of downtime, even if the load balancer is attached to an AWS Auto Scaling Group that has max and desired capacity set to 1, always register at least two target instances to the target group(s) associated with your ELBv2 load balancers.
To determine if your AWS ELBv2 load balancers distribute the traffic to at least two healthy target instances, perform the following actions:
To register additional healthy EC2 instances to the target group(s) associated with your ELBv2 load balancers, perform the following: