In 2006 we were building distributed applications that needed a master, aka coordinator, aka controller to manage the sub processes of the applications. It was a scenario that we had encountered before and something that we saw repeated over and over again inside and outside of Yahoo!.

For example, we have an application that consists of a bunch of processes. Each process needs be aware of other processes in the system. The processes need to know how requests are partitioned among the processes. They need to be aware of configuration changes and failures. Generally an application specific central control process manages these needs, but generally these control programs are specific to applications and thus represent a recurring development cost for each distributed application. Because each control program is rewritten it doesn’t get the investment of development time to become truly robust, making it an unreliable single point of failure.

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