Managing Failover

An active bonus is an amount that the BIG-IP system automatically adds to the overall HA score of an active traffic group or device. An active bonus ensures that the traffic group or device remains active when its score would otherwise temporarily fall below the score of the standby traffic group on another device. The active bonus that you configure can be in the range of 0 to 100.

A common reason to specify an active bonus is to prevent failover due to flapping, the condition where failover occurs frequently as a trunk member switches rapidly between availability and unavailability. In this case, you might want to prevent the HA scoring feature from triggering failover each time a trunk member is lost. You might also want to prevent the HA scoring feature from triggering failover when you make minor changes to the BIG-IP system configuration, such as adding or removing a trunk member.

For example, suppose that the HA group for a traffic group on each device contains a trunk with four members, and you assign a weight of 30 to each trunk. Without an active bonus defined, if the trunk on one device loses some number of members, failover occurs because the overall calculated score for that traffic group becomes lower than that of a peer device. You can prevent this failover from occurring by specifying an active bonus value.

The BIG-IP system uses an active bonus to contribute to the HA score of an active traffic group only; the BIG-IP system never uses an active bonus to contribute to the score of a standby traffic group.

To decide on an active bonus value, calculate the trunk score for some number of failed members (such as one of four members), and then specify an active bonus that results in a trunk score that is greater than or equal to the weight that you assigned to the trunk.

For example, if you assigned a weight of 30 to the trunk, and one of the four trunk members fails, the trunk score becomes 23 (75% of 30), putting the traffic group at risk for failover. However, if you specified an active bonus of 8 or higher, failover would not actually occur, because a score of 8 or higher, when added to the score of 23, is greater than 30.