@Override
    public LoadBalancerInstance provision(LoadBalancerSpec spec) {
        if ( ! spec.settings().isPublicEndpoint())
            throw new IllegalArgumentException("non-public endpoints is not supported with " + getClass());

        return new LoadBalancerInstance(Optional.of(DomainName.of(vipHostname)),
                                        Optional.empty(),
                                        Optional.empty(),
                                        Optional.empty(),
                                        Set.of(4443),
                                        Set.of(),
                                        spec.reals(),
                                        spec.settings(),
                                        List.of(),
                                        spec.cloudAccount());
    }
This implementation of {@link LoadBalancerService} returns the load balancer(s) that exist by default in the shared
routing layer.
<p>
Since such load balancers always exist, we can return the hostname of the routing layer VIP directly. Nothing has to
be provisioned.

@author ogronnesby
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/lb/SharedLoadBalancerService.java