HMM: A Cluster Membership Service

The Hidra Membership Monitor (HMM) is a distributed service that maintains the current set of active nodes in a cluster of machines. This protocol allows the detection of multiple machine joins or failures in a unique reconfiguration, using a low amount of messages (with a cost that is linear on the number of nodes). These membership services are needed to detect cluster changes as soon as possible, initiating then the reconfiguration of the cluster state, where support for replicated objects has been included. The HMM also manages and synchronises the reconfiguration steps needed by the kernel and Hidra components of each node, ensuring that all of them take the same steps at once. Thus, our system does not need an atomic multicast protocol to deliver the messages in these reconfiguration steps. All these services provide the basis to develop reliable intracluster transport protocols and to reduce the reconfiguration time of replicated objects and services.