nsync receives a message from the Cloud Controller when the user scales an app. It writes the number of instances into a DesiredLRP structure in the Diego BBS database.
BBS uses its convergence process to monitor the DesiredLRP and ActualLRP values. It launches or kills application instances as appropriate to ensure the ActualLRP count matches the DesiredLRP count.
Cell Rep monitors the containers and provides the ActualLRP value.