Failover server preference

PingDataSync supports endpoint failover, which is configurable using the location property on the external servers. By default, PingDataSync prefers to connect to and failover to endpoint servers in the same location as itself. If no location settings are configured, PingDataSync will iterate through the configured list of external servers on the Sync Source and Sync Destination when failing over.

PingDataSync does not perform periodic health checks of external servers, and does not failover automatically to a preferred external server. Because of the cost of sync failover, PingDataSync remains connected to a given server until the server stops responding or until the Sync Pipe is restarted. When a failover occurs, PingDataSync returns to the most preferred server, optionally using location settings to identify it, and works its way down the list. Here is an example configuration of external servers:

If the austin1 server were to become unavailable, PingDataSync will automatically pick up changes on the next server on the list, london1. If london1 is also down, then the next server, boston1, will be picked up. After PingDataSync iterates through the list, it returns to the top of the list. If PingDataSync is connected to london2 and it goes down, it will fail over to austin1.

To minimize WAN traffic, configure the location property for each external server using the dsconfig command on PingDataSync. Assume that PingDataSync has its own location property (set in the Global Configuration) set to "austin."

With the location property set for each server, PingDataSync gets its changes from server austin1. If austin1 goes down, PingDataSync will pick up changes from austin2. If austin2 goes down, the server will iterate through the rest of the list in the order it is configured.

The location property has another sub-property, preferred-failover-location that specifies a set of alternate locations if no servers in this location are available. If multiple values are provided, servers are tried in the order in which the locations are listed. The preferred-failover-location property provides more control over the failover process and allows the failover process to jump to a specified location. Care must be used so that circular failover reference does not take place. Here is an example configuration:

PingDataSync will respect the preferred-failover-location. If it cannot find any external servers in the same location as itself, it will look for any external servers in its own preferred-failover-location. In this example, when austin1 becomes unavailable, it will fail over to austin2 because they are in the same location. If austin2 is unavailable, it will fail over to boston1, which is in the preferred-failover-location of PingDataSync. If boston1 is unavailable, PingDataSync will fail over to boston2, and finally, it will try the london1 and london2 servers.