Traffic not returning to higher priority group on BIG-IP LTM

Hi all,

 

I was wondering if anyone else has seen this issue, or knows what might cause it.

 

The setup is; a single node in priority group 10, and two nodes in priority group 1. Load balancing method is 'round robin' and the priority activation is set to 'less than 1 active member'. We also have 'source_addr' set for persistence on the VIP. Everything else is pretty much default.

 

So, we had a situation where the single node in priority group 10 went offline, this caused all traffic to go to the two nodes in group 1 (as expected), but when the single node came back online, new connections were not being redirected to that preferred node. All connections were still being sent to the two nodes in group 1. We waited for quite some time to see if things would move back to the preferred node, but it wasn't. It wasn't until we forced the two nodes offline that we started to see connections being made on the preferred node.

 

I understand that some persistent connections will stay with the two nodes in the lower priority group until they time out, or get reset, but the LTM was sending new connections to them as well. We didn't observe any new connections being established on the preferred node after it came back online.

 

Is this a bug? Or is there some other setting we missed that could cause this behavior?

 

We're running ver: BIG-IP 11.2.1 Build 1299.0 Hotfix HF12

 

Any thoughts or suggestions would be greatly appreciated.

 

Thanks