I "inherited" an unmanaged EKS cluster with two nodegroups created through eksctl with Kubernetes version 1.15. I updated the cluster to 1.17 and managed to create a new nodegroup with eksctl and nodes successfully join the cluster (i had to update aws-cni to 1.6.x from 1.5.x to do so). However the the Classic Load Balancer of the cluster marks my two new nodes as OutOfService.
I noticed the Load Balancer Security Group was missing from my node Security Groups thus i added it to my two new nodes but nothing changed, still the nodes were unreachable from outside the EKS cluster. I could get my nodes change their state to InService by applying the Security Group of my two former nodes but manually inserting the very same inbound/outbound rules seems to sort no effect on traffic. Only the former nodegroup security group seems to work in this case. I reached a dead end and asking here because i can't find any additional information on AWS documentation. Anyone knows what's wrong?