[Beowulf] seamless failover

[HUSTKJH]

 Hi, all!
I am desiging a HA system for VoIP server cluster now.
My system should support fault tolerance with seamless failover feature.
I first begin with 2 nodes, and using Linux HA heartbeat package.
A lot of existing HA clusters are based on Linux HA heartbeat, but it doesn't support seamless failover/failback at present.
A lot of academic research papers address this problem (kernel-level, log-based...), but not in practice,and complicated and limited in the realization.
Linux HA is somewhat simple and easy-to-use, but don't know how to extend and change to support seamless failover.
Does anyone have related experience or good ideas...?
Or, are there any other open-source s/w for this?

Thanks.
John Peter
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