A fault tolerant system for a highly scalable distributed processing system in which fault tolerant groups (hereafter referred to as “FT groups”) are formed based on the functionalities of applications. A given FT group includes instances of the same applications and also different applications that perform the same function. The instances within the FT group are ranked as a primary and mirrors, which descend in rank. When the primary instance in the FT group crashes, that is, fails or becomes otherwise unavailable, the system utilizes the next ranking available (running) instance in the FT group as the primary instance. The change over to the next ranking mirror application is performed quickly and without loss of functionality through an exchange of “FT messages” under the control of a central monitoring and change-over control sub-system.