Health check of ELB Node

You are correct that AWS automatically manages the health of Application Load Balancer (ALB) nodes and updates DNS records accordingly. However, there's no need to create manual health checks in Route 53 for the ALB DNS name or individual IP addresses from each Availability Zone (AZ).

The ALB performs its own health checks on the registered targets (such as EC2 instances) in your target groups. When an AZ or ALB node becomes unhealthy, AWS automatically removes the corresponding IP addresses from the DNS record for the load balancer. This process, known as DNS failover, ensures that client requests are only routed to healthy ALB nodes in healthy AZs.

The recommendation for subnet sizing (at least a /27 bitmask with 8 free IP addresses) is to ensure that the ALB has enough IP addresses to scale and manage its nodes effectively. This is handled internally by AWS and doesn't require any additional configuration on your part.

Creating manual health checks in Route 53 for the ALB or its individual IP addresses is unnecessary and not recommended. The ALB's built-in health checking and DNS failover mechanisms are designed to handle high availability and fault tolerance without requiring additional manual intervention.

If you need to monitor the overall health of your ALB from an external perspective, you can create a Route 53 health check for the ALB's DNS name. However, this is typically only necessary for complex routing scenarios or when you need to integrate the ALB's health into a larger monitoring system. For most use cases, relying on the ALB's built-in health management is sufficient.
Sources
Health checks for Application Load Balancer target groups - Elastic Load Balancing
HealthCheck - Elastic Load Balancing
[Launch Announcement] Health Check Improvements for AWS Gateway Load Balancer | AWS re:Post
Health checks for the instances for your Classic Load Balancer - Elastic Load Balancing