Public IPv4 address costs since Feb 1st - ELBs use multiple service managed public IPs?

Hi,

Elastic Load Balancers (ELB) have the ability to dynamically scale in and out in response to/to handle the amount of traffic being processed by the load balancer. Per AWS Documentation -

As traffic to your application changes over time, Elastic Load Balancing scales your load balancer and updates the DNS entry. The DNS entry also specifies the time-to-live (TTL) of 60 seconds. This helps ensure that the IP addresses can be remapped quickly in response to changing traffic.

You can also find more details on the Scaling behavior in this article - https://aws.amazon.com/articles/best-practices-in-evaluating-elastic-load-balancing/

One way to validate is to run a DNS query for the public ALB endpoint DNS name, it may return the multiple IP addresses that you see in IPAM.

EDIT: I omitted the more likely root cause of the multiple Public IPs - if the public ALB is deployed into multiple AZs, each ALB node will have an ENI in each target AZ and each ENI will have a public IP address.

I checked my network interfaces for the ELB.

The 2 classic ELBs have two ENIs each in one AZ, and the 1 application ELB has 2 ENIs in each AZ.

Is it possible to have only 1 ENI on 1 AZ for 1 ELB, no redundancy? Why does app ELB have 2 ENIs in the same AZ?

EDIT: I omitted the more likely root cause of the multiple Public IPs - if the public ALB is deployed into multiple AZs, each ALB node will have an ENI in each target AZ and each ENI will have a public IP address.

Thanks, this might be it! Will look into it and how to remove the LB from the other AZs