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Posted 4 Mar 2013

Managing server failover in WCF

, 4 Mar 2013
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In this article I will talk about server failover and how to manage it.

Sample Image


In this article I will talk about server failover and how to manage it.

Solution Summary

Here is the message sequence diagram for a vanilla case.

Sample Image - maximum width is 600 pixels

Here is the problematic scenario that we are going to solve:

  • Concurrency problem. In our case it could happen that some services send messages at the same time. This problem will be solved with the Vector Clock algorithm.
  • Critical section - System activation should be performed in the critical section.

Pseudo code

procedure OnMessageArrived(msg)
    isGreater = msg.VectorClockTimeStamp > currentVectorClockTimeStamp
    isLess = msg.VectorClockTimeStamp < currentVectorClockTimeStamp

    if ( isGreater ) then
        currentClockTimeStamp = msg.VectorClockTimeStamp
    else if ( isLess == false )
         concurrency error 
    end if    
    call appropriate message handler
procedure Activate(msg)
    if ( AcquireLockFromAllServicesApproved() ) then
        isActivated = true
    End if

procedure Deactivate(msg)
    isActivated = false

//message handlers     

procedure HandleHeartBeatFromOther(msg)
    //do something

procedure HandleOtherSystemAcquiredLock(msg)
    if (CurrentSystemInLock)
        return LockNotAprooved;
        return LockAprooved;
    End if
procedure HandleOtherSystemReleasedLock(msg)
    //do something


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This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Dima Zevelev
Software Developer (Senior) Better Place
Israel Israel
No Biography provided

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