[EKS] [request]: configurable target group for kube service of type LoadBalancer

[ausmith]

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Tell us about your request
The ability for a kube service object of type LoadBalancer to configure what nodes to add to target groups based upon a node selector. This would allow large shared clusters with multiple node groups/autoscaling groups to avoid having ALL nodes get added to a given target group.

Which service(s) is this request for?
EKS

Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?
As long as we are using node ports for the connectivity between a load balancer created by a service of type LoadBalancer (see #981 for an alternative approach to today's host port solution) and the applications, all nodes within the kube cluster are getting added to the target group. This presents issues if there are multiple node groups/autoscaling groups within a given cluster (e.g. for segmentation or different workload types) as a given application likely does not run on all nodes.

Being able to define a node selector on the service for the target group to use could significantly cut down unnecessary target group membership and hence simplify reasoning about what network connectivity is available between a cluster and load balancers.

Are you currently working around this issue?
No

Additional context
N/A

Attachments
N/A

[mikestef9]

The recently released AWS Load Balancer Controller includes support NLB IP targeting #981. If you are using the VPC CNI plugin and can directly target pods, this can optimize the size of target groups in large clusters.

Additionally, a recent upstream feature merged adds support for filtering load balancer target nodes, and this will be available once EKS supports version 1.19.