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manc_63343's avatar
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Jan 12, 2011

forward to a different pool when pool is down

Is there an easy way to forward http requests to a different Vip when the Vip is marked down. for eg: it's the case when everything on that pool turns "red" and there still are some client connections trying to hit which we want to re-direct/forward to another pool or vip in other data center. This will help us solve for those clients connections that cache connections for little longer than expected. Once they resolve from GTM everything wil stop coming to first data center.

4 Replies

  • Hi Manc,



    The pool setting 'action on service down' is the closest I can think of to change the LTM behavior for handling existing connections when the current pool member is marked down by a monitor. Note that you can't send an HTTP redirect as the HTTP request/response cycle could be in any state. In other words, you couldn't send an HTTP redirect after LTM was already proxing the response content. However, a reset might force the client to resend the request (or hit refresh to manually resend the request).




    Specifies how the system should respond when the target pool member becomes unavailable. The default is None.



    * None: Specifies that the system does not select a different node. Selecting None causes the system to send traffic to the node even if it is down, until the next health check is done.


    * Reject: Specifies that the system sends an RST or ICMP message.


    * Drop: Specifies that the system simply cleans up the connection.


    * Reselect: Specifies that the system selects a different node. Selecting Reselect causes the system to send traffic to a different node after receiving the message that the original node is down.




  • Thanks! Does this mean that GTM will still LTM vip as down (which is what we want)?



    Also, we have another LTM vip on other data center. Can we specify that vip in "Reselect"? OR do we need to create another pool in same LTM with reals from other data center and do that way?



    Is there any other better way of doing this? This is what we really are trying to achieve:



    1. Since we don't have write access to GTM only way we change the GTM to make other site "Active" is by asking someone on network team to do it for us. We have around 40 WIPs and it becomes very difficult that route.


    2. We already have health checks on LTM that are http health checks. These health checks look for string say "up" for every vip. We can easily turn that off to mark vip down. This causes GTM to make other site Active. It works great. The only problem


    is that clients that are caching connections get reset causing customer impact. We can avoid this since at this point we have healthy reals but only doing failover for the purpose of ease.



    So I was thinking if there is any way to re-direct clients to the other site or something else where they don't get connection reset but transparently connect to other data center.


  • Hi Manc,


    Yes it shouldn't impact the GTM from what it's doing now - at least from what I can tell. However, If you are running version 10 on both data center you can pair up the LTMs via Tunnel. F5 calls this setup iSession. Click Here to see additional information of how it can be set up.




    I hope this helps,


  • For this purpose can I use Fallback feature on LTM istead of LB::reselect? Sounds much simpler and easier.