Entera middleware is reliable and fault-tolerant. Entera’s load-balancing capabilities, accomplished through “server-clustering,” also enable it to support fault-tolerance. One of Entera’s first demos was always to “pull the plug” on a server machine and watch it’s clients transparently go to the next server machine on the next request.
The basic characteristics of fault tolerance require:
- No single point of failure
- No single point of repair
- Fault isolation to the failing component
- Fault containment to prevent propagation of the failure
- Availability of reversion modes
In addition, fault tolerant systems are characterized in terms of both planned service outages and unplanned service outages. These are usually measured at the application level and not just at a hardware level. The figure of merit is called availability and is expressed as a percentage. A five nines system would therefore statistically provide 99.999% availability.
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