Recovery after a link failover and controlling primary unit selection (controlling falling back to the prior primary unit)
If you find and correct the problem that caused a link failure (for example, re-connect a disconnected network cable) the cluster updates its link state database and re-negotiates to select a primary unit.
What happens next depends on how the cluster configuration affects primary unit selection:
- The former primary unit will once again become the primary unit (falling back to becoming the primary unit)
- The primary unit will not change.
As described in An introduction to the FGCP on page 1310, when the link is restored, if no options are configured to control primary unit selection and the cluster age difference is less than 300 seconds the former primary unit will once again become the primary unit. If the age differences are greater than 300 seconds then a new primary unit is not selected. Since you have no control on the age difference the outcome can be unpredictable. This is not a problem in cases where its not important which unit becomes the primary unit.