ALB is only registered to 2 subnets after upgrading to v2.7.2

[jmtsi]

Describe the bug
After upgrading the ALBC to v2.7.2, only 2 of our 3 correctly-annotated subnets are registered to ALB, which causes some of the ip-targets to have status Unused with an error: Target is in an Availability Zone that is not enabled for the load balancer

Steps to reproduce
Create an ingress without specifying annotation alb.ingress.kubernetes.io/subnets. A new ALB gets created, but only having 2 of the 3 subnets.

Expected outcome
The load balancer gets created with all 3 subnets that have the label kubernetes.io/role/internal-elb=1

Environment
Kubernetes: 1.29.1
ALBC: v2.7.2
EKS platform version: eks.6

Additional Context:
I tried to find anything subnet-discovery related from ALBC debug logs, but found nothing.

As a workaround, I added the alb.ingress.kubernetes.io/subnets annotation with a list of all 3 subnets, which fixed the issue for now.

Full list of annotations used:
alb.ingress.kubernetes.io/backend-protocol: HTTP
alb.ingress.kubernetes.io/healthcheck-path: /ping
alb.ingress.kubernetes.io/ip-address-type: dualstack
alb.ingress.kubernetes.io/listen-ports: [{"HTTP": 80}]
alb.ingress.kubernetes.io/load-balancer-attributes: routing.http2.enabled=false
alb.ingress.kubernetes.io/scheme: internal
alb.ingress.kubernetes.io/target-group-attributes: load_balancing.algorithm.type=round_robin
alb.ingress.kubernetes.io/target-type: ip
kubernetes.io/ingress.class: alb

[aravindsagar]

Hi! Thanks for reporting the issue. Can you please let us know which version were you using prior to 2.7.2? Controller logs would also be helpful. Thanks!