Linux-HA Heartbeat System Design

One of the most commonly identified features which is felt to be necessary for Linux to be considered "enterprise−ready" is High−Availability. High−Availabil− ity (HA) systems provide increased service availability through clustering techniques. HA clusters minimize availability interruptions by quickly switching services over from failed systems to working systems, providing the customer with an illusion of con− tinuous availability. As such, high−availability features, are vital to mission−critical systems. Although there are many components to a high−availability system, two of the key components are heartbeat services and cluster communication services. Heartbeat services provide notification of when nodes are working, and when they fail. In the Linux−HA project, the heartbeat program provides these services and intracluster com− munication services. This paper describes the design of the heartbeat program which is part of the High−Availability Linux Project with particular emphasis on the rationales behind key design choices, and the results obtained.