Ensure that the EC2 instances (targets) registered to your Amazon Application Load Balancers (ALBs) and Network Load Balancers (NLBs) are evenly distributed across all Availability Zones (AZs) in order to improve the reliability of your load balancers configuration.
Having a balanced distribution of target instances across all Availability Zones will improve the availability and reliability of the application(s) behind your load balancers (ELBv2). The more Availability Zones assigned and greater the spread, the better redundancy and availability within your load balancing environment.
To determine if the EC2 target instances registered to your load balancers are distributed evenly across all assigned Availability Zones, perform the following actions:
To equally distribute your existing EC2 target instances across all Availability Zones within the selected AWS region, you need to add new Availability Zones to the ELBv2 load balancer configuration and migrate the registered instances between these AZs. To implement this method, perform the following actions:Note: As example, this section demonstrates how to add a new AZ named us-east-1c to an existing AWS Application Load Balancer configuration and migrate a Linux EC2 instance from us-east-1b to the newly added AZ, i.e. us-east-1c, within the US East (N. Virginia) region: