public KubernetesEndpointGroupBuilder portName(String portName) {
        this.portName = requireNonNull(portName, "portName");
        return this;
    }
Sets the name of the <a href="https://kubernetes.io/docs/concepts/services-networking/service/#field-spec-ports">port</a>
from which <a href="https://kubernetes.io/docs/concepts/services-networking/service/#type-nodeport">NodePort</a>
should be fetched from. If not set, the first node port will be used.
kubernetes/src/main/java/com/linecorp/armeria/client/kubernetes/endpoints/KubernetesEndpointGroupBuilder.java