Group communication is an essential building block for the development of fault-tolerant distributed applications. The AspectIX group communication system (AGC) is a reconfigurable totally-ordered group communication system based on distributed consensus algorithms.

Our novel design uses a policy-based mechanism for dynamical reconfiguration of the system at runtime without service interruption. Reconfigurations may optimize for most efficient ``best-case'' operation or for minimal delays in failure situations, may select different failure models like crash-stop, crash-recovery, or Byzantine, and may adjust internal parameters like timeout values for failure detection.

An instance of a distributed consensus algorithm is used for providing total order of messages. Various algorithm instances, like the classic and Byzantine variant of Paxos, can be configured for a specific group communication instance. Mechanisms to adjust the set of participating nodes at runtime in a safe way are provided.

The group communication system is the core element of the fault tolerance support in AspectIX