public Server getServerFromLoadBalancer(@Nullable URI original, @Nullable Object loadBalancerKey) throws ClientException {
        String host = null;
        int port = -1;
        if (original != null) {
            host = original.getHost();
        }
        if (original != null) {
            Pair<String, Integer> schemeAndPort = deriveSchemeAndPortFromPartialUri(original);        
            port = schemeAndPort.second();
        }

        // Various Supported Cases
        // The loadbalancer to use and the instances it has is based on how it was registered
        // In each of these cases, the client might come in using Full Url or Partial URL
        ILoadBalancer lb = getLoadBalancer();
        if (host == null) {
            // Partial URI or no URI Case
            // well we have to just get the right instances from lb - or we fall back
            if (lb != null){
                Server svc = lb.chooseServer(loadBalancerKey);
                if (svc == null){
                    throw new ClientException(ClientException.ErrorType.GENERAL,
                            "Load balancer does not have available server for client: "
                                    + clientName);
                }
                host = svc.getHost();
                if (host == null){
                    throw new ClientException(ClientException.ErrorType.GENERAL,
                            "Invalid Server for :" + svc);
                }
                logger.debug("{} using LB returned Server: {} for request {}", new Object[]{clientName, svc, original});
                return svc;
            } else {
                // No Full URL - and we dont have a LoadBalancer registered to
                // obtain a server
                // if we have a vipAddress that came with the registration, we
                // can use that else we
                // bail out
                if (vipAddresses != null && vipAddresses.contains(",")) {
                    throw new ClientException(
                            ClientException.ErrorType.GENERAL,
                            "Method is invoked for client " + clientName + " with partial URI of ("
                            + original
                            + ") with no load balancer configured."
                            + " Also, there are multiple vipAddresses and hence no vip address can be chosen"
                            + " to complete this partial uri");
                } else if (vipAddresses != null) {
                    try {
                        Pair<String,Integer> hostAndPort = deriveHostAndPortFromVipAddress(vipAddresses);
                        host = hostAndPort.first();
                        port = hostAndPort.second();
                    } catch (URISyntaxException e) {
                        throw new ClientException(
                                ClientException.ErrorType.GENERAL,
                                "Method is invoked for client " + clientName + " with partial URI of ("
                                + original
                                + ") with no load balancer configured. "
                                + " Also, the configured/registered vipAddress is unparseable (to determine host and port)");
                    }
                } else {
                    throw new ClientException(
                            ClientException.ErrorType.GENERAL,
                            this.clientName
                            + " has no LoadBalancer registered and passed in a partial URL request (with no host:port)."
                            + " Also has no vipAddress registered");
                }
            }
        } else {
            // Full URL Case
            // This could either be a vipAddress or a hostAndPort or a real DNS
            // if vipAddress or hostAndPort, we just have to consult the loadbalancer
            // but if it does not return a server, we should just proceed anyways
            // and assume its a DNS
            // For restClients registered using a vipAddress AND executing a request
            // by passing in the full URL (including host and port), we should only
            // consult lb IFF the URL passed is registered as vipAddress in Discovery
            boolean shouldInterpretAsVip = false;

            if (lb != null) {
                shouldInterpretAsVip = isVipRecognized(original.getAuthority());
            }
            if (shouldInterpretAsVip) {
                Server svc = lb.chooseServer(loadBalancerKey);
                if (svc != null){
                    host = svc.getHost();
                    if (host == null){
                        throw new ClientException(ClientException.ErrorType.GENERAL,
                                "Invalid Server for :" + svc);
                    }
                    logger.debug("using LB returned Server: {} for request: {}", svc, original);
                    return svc;
                } else {
                    // just fall back as real DNS
                    logger.debug("{}:{} assumed to be a valid VIP address or exists in the DNS", host, port);
                }
            } else {
                // consult LB to obtain vipAddress backed instance given full URL
                //Full URL execute request - where url!=vipAddress
                logger.debug("Using full URL passed in by caller (not using load balancer): {}", original);
            }
        }
        // end of creating final URL
        if (host == null){
            throw new ClientException(ClientException.ErrorType.GENERAL,"Request contains no HOST to talk to");
        }
        // just verify that at this point we have a full URL

        return new Server(host, port);
    }
Compute the final URI from a partial URI in the request. The following steps are performed:
<ul>
<li> if host is missing and there is a load balancer, get the host/port from server chosen from load balancer
<li> if host is missing and there is no load balancer, try to derive host/port from virtual address set with the client
<li> if host is present and the authority part of the URI is a virtual address set for the client, 
and there is a load balancer, get the host/port from server chosen from load balancer
<li> if host is present but none of the above applies, interpret the host as the actual physical address
<li> if host is missing but none of the above applies, throws ClientException
</ul>

@param original Original URI passed from caller
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/LoadBalancerContext.java