Cluster has preemption enabled for F5




Preemption is generally a bad idea in clustering, although sometimes it is the default setting. Indeni will alert if it's on.

Remediation Steps

It is generally best to have preemption disabled. Instead, once this device returns from a crash, you can conduct the failover manually.

How does this work?

This script uses the F5 iControl API to retrieve the traffic group configuration to determine if auto failback is enabled or not.

Why is this important?

Preemption, or auto failback as F5 calls is, is a function in clustering which sets a primary member of the cluster to always strive to be the active member. The trouble with this is that if the active member that is set with preemption on has a critical failure and reboots, the cluster will fail over to the secondary and then immediately fail over back to the primary when it completes the reboot. This can result in another crash and the process would happen again and again in a loop. It is generally a good idea not to have the preemption feature enabled.

Without Indeni how would you find this?

An administrator would have to log in to his devices via the Web interface and verify that the auto failback option is not set. This could also be detected the hard way during an upgrade of a redundant pair if a recently upgraded node takes over prematurely.

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