I think your question is about using LB properties (IP, port, hostname) inside the cartridge instance. We can pass those parameters in the cartridge definition as payload parameters as a simple solution. We can also publish those information in meta-data service as well. Publishing to meta-data service will be more flexible since we can easily update those values without having to redeploy cartridges etc.
Regarding Kubernetes scenario, we need to have an external LB which would forward requests to all the upstream minion instances. Then use that external LB within all pods (services can be differentiated through different hsotnames)
This is just my suggestion. Perhaps there is a better way.