and the host where the application is running etc. These labels are all available to be expressed in the label-selector carried by a service reference. A service in the registry can be made accessible to clients by creating a service reference. A client would then be able to reach the service at the reference’s name (IP:port). Now let’s look at how AppSwitch guarantees that the reference remains valid even when the target service has not yet come up.</p><h3 id=non-blocking-requests>Non-blocking requests