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bapho1337_25353's avatar
bapho1337_25353
Icon for Nimbostratus rankNimbostratus
Mar 09, 2016

LTM Policy - LB does still use a policy rule with an forward to pool action when all pool members are down

Dear all,

 

I've a strange behavior with my LTM running on 11.5.1HF5.

 

The following polices are currently configured :

 

Strategy : First Match Requires : HTTP Controls : Forwarding

 

Rules deployed:

 

Rule 1 | http-uri path starts-with /test/production1 = Action forward select pool /Common/prodpool1

 

Rule 2 | http-uri path starts-with /test/production2 = Action forward select pool /Common/prodpool2

 

Rule 3 | http-uri path starts-with /test/production3 = Action forward select pool /Common/prodpool3

 

Rule 4 | http-uri path not starts-with /test/production1

 

Rule 4 | http-uri path not starts-with /test/production2

 

Rule 4 | http-uri path not starts-with /test/production3

 

Rule 4 | = Action forward select pool /Common/prodpool4

 

Every pool just consists of one pool member, because of https://support.f5.com/kb/en-us/solutions/public/14000/900/sol14968.html

 

So we have pools configured as follows :

 

prodpool1 = prodnode1 prodpool2 = prodnode2 prodpool3 = prodnode3 prodpool4 = prodnode4

 

All those 4 nodes are still within a common pool called prodpool_all which is bound to the VIP as default pool.

 

Now for the problem :

 

If for example prodpool4 goes down ( because prodnode4 is down ), the loadbalancer is still forwarding traffic to this node, as the counters for the default pool ( prodpool_all) are not raising up. Therefore we can still see that the "Invoked" and "Suceeded" counters for Rule4 are counting up.

 

From my understanding i would have thought that if a pool which is used within a policy rule, this rule will no longer be evaluated. Can someone light up the darkness here ? Do we miss something here ?

 

Btw we also tried creating a catch-all rule at last ( with forward action -> prodpool_all ) and changed the strategy vom First-Match to All and Best, but that doesn't helped a bit.

 

Thanks a lot for your help

 

Best Regards

 

Christopher

 

application delivery
BIG-IP
LTM

1 Reply

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  • Kai_Wilke's avatar
    Kai_Wilke
    Icon for MVP rankMVP
    Mar 09, 2016

    Hi Christopher,

     

    the LTM policy based pool selection will not care about the availability of the pool. It would just select the pool as specified by you policy and also won't skip any rules.

     

    But your requirement can be solved by using the Priority Group & Priority Group Activation features.

     

    https://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-concepts-11-1-0/ltm_pools.html1216212

     

    Simply add each of your nodes to each of your pools and then increase the priority of the "default" node. In this case the request will be only send to the default node. And if this node is marked down, then the remaining pool will be used as fallback.

     

    Note: In a best-match/first-match strategy you don't need to exclude the already processed URI (see your Rule 4). Just let the rule order or best-match engine do their work...

     

    Cheers, Kai