Improvement for the error log while Subnet Discovery failed

[guessi]

Is your feature request related to a problem?

Currently, AWS-LBC would have the following error log emit (as follow) if it failed to do Subnet Discovery. However, with unclear error log, it is hard to identify which tag it is looking for.

{
  "level": "error",
   ...
  "msg": "Reconciler error",
   ...  
  "error": "couldn't auto-discover subnets: unable to resolve at least one subnet (0 match VPC and tags)"
}

Code block to be improved:

• https://github.com/kubernetes-sigs/aws-load-balancer-controller/blob/v2.6.2/pkg/networking/subnet_resolver.go#L192-L203

Describe the solution you'd like

While user is trying to create internal Load balancer, but having kubernetes.io/role/elb: 1 tagged but having no kubernetes.io/role/internal-elb tagged. It is quite confusing to get "unable to resolve at least one subnet (0 match VPC and tags)", would be better to have "which tag" it is looking for to let user more easily to find out the missing tag is kubernetes.io/role/internal-elb: 1.

It would be better to have tag key included in the error log.

Expected results:

• For the error of internal load balancer reconciler error:

"error": "couldn't auto-discover subnets: unable to resolve at least one subnet (0 match VPC and tags: [kubernetes.io/role/internal-elb])"

• For the error of internet-facing load balancer reconciler error:

"error": "couldn't auto-discover subnets: unable to resolve at least one subnet (0 match VPC and tags: [kubernetes.io/role/elb])"

Describe alternatives you've considered

n/a