By default, if a target is unavailable (that a request would typically be directed to) - that is, the server is down - the request is directed to the next best available alternative target. When the original target becomes available, it is set into rotation after the specified timeout or failover. However, if needed it is possible to set a Failure Delay. Failure Delay is very important in Exchange data centers.

Implementing an Exchange data center failover is not a trivial event - it is not recommended to automatically failover upon detection of a site failure. Delaying the failover for a short period ensures that failovers do not occur because of trivial and temporary failures.

Delaying the failover can also provide the Exchange administrators time to ensure that the secondary site is ready to provide the requisite levels of service.

The LoadMaster provides a Failure Delay option which, when enabled, delays a failover occurring for a configurable period of time after a site failure is detected. If, after the delay, the site recovers, the failover is not initiated. If the site has not recovered, the failover is initiated as per normal.

If a Failure Delay is set, another option becomes available underneath it – Site Recovery Mode. If an endpoint fails the health check it is marked as "failing". After the Failure Delay time ends, the endpoint is marked as down. The Site Recovery Mode determines what recovery options are implemented when a failed site recovers.

  • Automatic - when the endpoint recovers (passes the health check), the endpoint is marked as up and the LoadMaster automatically makes the endpoint available for use

  • Manual - upon failure, the endpoint is administratively disabled and is not available for use until you click Enable for the relevant endpoint and the health check is passing.