Private IP requirements in VPC for Application Load Balancer

Question

How many private IP's does internal ALB need per subnet for creation?

Is it possible to figure out which IP's are allocated and can they be static, so that the AWS customer can create firewall rules from on-prem to this VPC? For example, via their Direct Connect to private VPC subnets.

Accepted Answer

As called out in the [docs](https://docs.aws.amazon.com/elasticloadbalancing/latest/application/application-load-balancers.html):

> To ensure that your load balancer can scale properly, verify that each Availability Zone subnet for your load balancer has a CIDR block with at least a /27 bitmask (for example, 10.0.0.0/27) and at least 8 free IP addresses. Your load balancer uses these IP addresses to establish connections with the targets.

For the 2nd part of the question you can use the approach listed in this blog post [Using static IP addresses for Application Load Balancers](https://aws.amazon.com/blogs/networking-and-content-delivery/using-static-ip-addresses-for-application-load-balancers/)

Private IP requirements in VPC for Application Load Balancer

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