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Andy_McGrath's avatar
Andy_McGrath
Icon for Cumulonimbus rankCumulonimbus
Jul 08, 2014

GTM Sync Group, sharing state information

Have a design where two GTMs are located in two different data centres and configured in a Sync Group. Then each Data Centre has a single LTM (currently in Pre-Production, production will have a HA pair), each GTM can only monitor the local LTM only and is unable to monitor the LTM in the other Data Centre. All monitoring is using bigip.

 

My understanding was that a GTM sync group shared state information so if one GTM monitor for a LTM fails but another succeeds the LTM (server) and all Virtual Servers will be marked as online. What I am seeing is each GTM is marking the local LTM (Server) as up and the remote LTM as down and only issuing IPs for the local data centre.

 

Any one able to confirm the default behaviour of the GTMs in this design?

 

Running version 11.4.1

 

availability
BIG-IP DNS
design

4 Replies

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  • shaggy's avatar
    shaggy
    Icon for Nimbostratus rankNimbostratus
    Jul 08, 2014

    You generally want all GTMs communicating with each other and all LTMs (not just local) via iquery. The GTM will delegate monitoring of virtual servers to the device that it thinks is best - in the case of virtual servers, it will delegate monitoring to the LTM on which they are configured.

     

    http://support.f5.com/kb/en-us/products/big-ip_gtm/manuals/product/gtm-implementations-11-4-0/1.html

     

    From my experience, it is best to allow all GTMs to talk to all LTMs in order to have resilient monitoring. If my GTM in DC1 fails, I don't necessarily want all applications to fail to DC2.

     

  • Andy_McGrath's avatar
    Andy_McGrath
    Icon for Cumulonimbus rankCumulonimbus
    Jul 09, 2014

    Understand all GTMs should communicate with all LTMs but need to confirm the expected default behaviour. Will a GTM that cannot communicate with an LTM via iQuery still show the LTM (server) and the virtual servers as online and issue IP addresses as long as another GTM's iQuery is successfull? Or will that single GTM mark the server and virtual server as down and stop issuing IPs?

     

  • shaggy's avatar
    shaggy
    Icon for Nimbostratus rankNimbostratus
    Jul 09, 2014

    I believe that, because the LTM and associated virtual servers are using the bigip monitor, expected behavior is that the local GTM will fail all virtual server objects hosted on the LTM that it cannot reach via iquery (you should validate with F5 support) regardless of the other GTM's status.

     

    If this isn't desired, you can use other monitors in addition to the bigip monitor that can operate in the manner that you described. For example, if you assign an additional HTTP monitor to a GTM virtual server object, the GTM will delegate that monitor duty to another F5 device in that virtual server's data center. If the GTM loses connectivity to the delegated monitoring F5 device, it can use another live F5 in that data center to monitor that virtual server object.

     

  • Andy_McGrath's avatar
    Andy_McGrath
    Icon for Cumulonimbus rankCumulonimbus
    Jul 09, 2014

    Talked to F5 Support and confirmed this is by design.

     

    The LTMs send (F5 Support said "broadcasts") status/monitor updates to all GTMs via iQuery, if the iQuery connection fails or is missing for the bigip monitor timeout period then the GTM will mark the LTM (server) down and all associated Virtual Servers.

     

    Shaggy is correct you can use other monitoring for the Virtual Servers which can be delegated to another F5.

     

    Not how I originally understood GTM sync group bigip monitor communication to work but I have been educated :)