Directory Proxy Server can also be used to protect a replicated directory service from failure due to a faulty client application. To improve availability, a limited set of masters or replicas is assigned to each application.
Suppose a faulty application causes a server shutdown when the application performs a specific action. If the application fails over to each successive replica, a single problem with one application can result in failure of the entire replicated topology. To avoid such a scenario, you can restrict failover and load balancing of each application to a limited number of replicas. The potential failure is then limited to this set of replicas, and the impact of the failure on other applications is reduced.