[Feature request]: Declarative defaults for subnets selected when there are multiple qualified #4046
Description
Describe the feature you are requesting
The ability the set default subnets that AWS Loadbalancer chooses, when there are multiple subnets to choose from.
Motivation
We have EKS clusters that span multiple subnets for different functions. e.g. Application, Database, Proxies etc. Most of our services are configured with an annotation, so they choose the correct subnet, but occasionally a service slips by without this annotation. This causes AWS loadbalancer controller to choose a subnet for the service in less then desirable fashion, as described here:
https://github.com/kubernetes-sigs/aws-load-balancer-controller/blob/57472c44170f0f75df67bb5b6e83b75a2db03231/docs/deploy/subnet_discovery.md?plain=1#L5C63-L6C25
Describe the proposed solution you'd like
Make it so we can configure a flag for "default" subnets that it selects. e.g. if you have the following subnets
subnet-a
subnet-b
subnet-c
subnet-d
you could choose subnet-c, subnet-d to be assigned as the subnets. Applications that would like to use subnet-a and subnet-b could do so by using the aws-load-balancer-subnets annotation
Describe alternatives you've considered
If this feature cannot be created, likely we will look into enforcing all service objects to declare the aws-load-balancer-subnets annotation via a policy tool like Kyverno
Contribution Intention (Optional)
-[ ] Yes, I am willing to contribute a PR to implement this feature
-[x] No, I cannot work on a PR at this time
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[-]More control on the selected subnets[/-][+][Feature request]: Declarative defaults for subnets selected when there are multiple qualified[/+]shraddhabang commentedon Feb 12, 2025
@devopsjourney1 Hey thanks for reaching out to us. I think this is a fair ask. Any community contributions are welcome for this.
1mwataru commentedon Feb 25, 2025
@shraddhabang (cc @devopsjourney1)
I'm planning to work on this Issue.
Currently, I'm thinking of adding a
--default-subnetsoption where we can specify desired subnets in an array to meet this requirement.I expect that this option may receive both public and private subnets, or sometimes just one AZ's subnets.
For these cases, I'm currently considering the following behavior:
Pick the appropriate subnets from
--default-subnetsbased on whether the ELB scheme is internet-facing or internalIf only one AZ's subnets remains after the above selection, pick the remaining required subnets from tagged subnets in lexicographical order (same as current behavior)
Please let me know if you have any thoughts on the proposed behavior or if you have any better suggestions.
Also, could you please assign this to me?
devopsjourney1 commentedon Feb 28, 2025
This behavior would work for me. Thank you.
1mwataru commentedon Mar 3, 2025
/assign