The easy way to do this is with NodePorts, wherein you configure your LB with all the nodes in your cluster being app servers on a certain port for a certain app. However you will lose some performance as there's some iptables magic under the hood.

Beyond that there's a sea of options for more native integrations that will depend on whether your LB vendor has an K8s integration, how friendly your networking team is, and how much code you're willing to write.

for baremetal you can use metallb or kube-router if you have bgp infra. no need for hardware ha lb