How does cluster computer work in a network? How do they send message to one another?

Cluster Computer, this technology used to maintain availability of server or computer fully(24 hours, 365 days). For this kind of support they configure the first server then they configure the second server with the same configuration. Both server connected over network(sometime both in geographically different location). The two server having same IP address with clustering software. Also there is additional network card in both computers. This maintained the Heart Beat of cluster server.

Suppose the first computer/server is the main one, whenever the main fails the second one going to be linked.

So the second computer always checks the Heart Beat of first server for each micro seconds, if heart beat fails the second going to be response the request over network.

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