5 Replies Latest reply: Sep 1, 2014 3:33 PM by dvohra21 RSS

    Query on Cluster behavior when multicast doesn't work.....

    Vijaya Moderator -Oracle

      Hi Everyone,

       

      I have a customer who has configured 4 managed servers and configured all servers to be part of Cluster and chosen Multicast option as Messaging type.

       

      Customer has some network issues in his environment, and found multicast test fails.. The network fragments doesn't reach some of the members of the cluster due to the network issue.

       

      However all the servers in the cluster have got synchronized successfully and joined cluster..

       

      Customer is worried that the cluster heart beats would be missed due to the network issue, however weblogic has not reported any incident in the logs , even after enabling the cluster debug flags, the behavior is still the same.

       

      Could you please let me know if it is right behavior?

       

      Does a cluster not fail if multicast  doesn't work in the weblogic environment ?

       

      Thanks in Advance,

      Vijaya

        • 1. Re: Query on Cluster behavior when multicast doesn't work.....
          dvohra21

          A server being multicast to does not distinguish between why a signal is not received, whether it is due the server failing or a network issue. If a signal is not received from a multicast server the server is marked as failed and the other servers stay in the cluster. If one of the four servers has network issue the other servers stay in the cluster.

           

          Does a cluster not fail if multicast  doesn't work in the weblogic environment ?


          The servers with network issue should be marked as failed and not join the cluster. Otherwise how would it be known that why a signal is not being received from a server, whether it is due to network issue or the server has actually failed.

          • 2. Re: Query on Cluster behavior when multicast doesn't work.....
            Vijaya Moderator -Oracle

            There is no issue in the logs and servers shows as running status. However the multicast test is failing....

             

            Even after enabling cluster debug flags, i couldn't find any single warning message in weblogic logs..

             

             

            regards,

            Vijaya

            • 3. Re: Query on Cluster behavior when multicast doesn't work.....
              dvohra21

              If the logs don't indicate the server is failing, the multicast test is not performed as required or has some other issue. Otherwise the cluster would have failed too.

              • 4. Re: Query on Cluster behavior when multicast doesn't work.....
                Gp-Oracle

                Hi Vijaya,

                 

                If one or two multicast messages lost, it doesn't really affect the cluster membership.

                 

                Internally Multicast Manager implements the heart beat mechanisam. It implements heartbeat retry protocal, if the multicast manager continuosly miss three heart beats then only server will be moved out of the cluster membership.

                 

                However, I would suggest customer to set the TTL values appropriately in their network also enable Message ordering enabled. If customer is in 11g, there are known issues make sure to suggest the respective patches. That will further help the customer to stable their environment.

                 

                Hope it helps.

                Regards,

                GP

                • 5. Re: Query on Cluster behavior when multicast doesn't work.....
                  dvohra21

                  If cluster spans several network paths or too many multicast packets are being lost Unicast is recommended. In Unicast each server has to inform only the Master not each other (as in Multicast).

                   

                   

                  For example, four servers WLS1, WLS2, WLS3, WLS4 with WLS1 as the Master. In Unicast each of the

                  WLS2, WLS3, WLS4 servers has to inform only the WLS1 server resulting in 3 network paths. In Multicast each of the WLS1, WLS2, WLS3, WLS4 has to inform each other resulting in 6 network paths.