The following illustrates a simplified synchronization topology with a single failover server on the source, destination, and PingDirectory Server, respectively. The gray lines represent possible failover connections in the event the server is down. The external servers are prioritized so that src1 has higher priority than src2; dest1 has higher priority than dest2.

The main PingDirectory Server and its redundant failover instance communicate with each other over LDAP and bind using cn=IntraSync User,cn=Root DNs,cn=config. The servers run periodic health checks on each other and share information on all changes that have been processed. Whenever the failover server loses connection to the main server, it assumes that the main server is down and begins processing changes from the last known change. Control reverts back to the main server once it is back online.

Unlike the PingDirectory Servers, the external servers and their corresponding failover server(s) do not run periodic health checks. If an external server goes offline, the failover server will receive transactions and remain connected to PingDirectory Server until the Sync Pipe is restarted, regardless of if the main external server comes back online.

PingDataSync Server in a simplified setup
PingDataServer Sample Failover