Flow Digest: A State Replication Scheme for Stateful High Availability Cluster

Stateful tracking is a popular technique in firewall filtering and state replication is used to provide reliable connectivity. This paper proposes a new approach for improving existing state replication protocols which ensure state consistency amongst the nodes of a stateful HA cluster. Our goal is to develop a new scheme which reduces the update overhead in the face of both low and high connection loads in order to maximize the capacity and scalability of a high availability cluster. A new representation called flow digest is proposed. Also the ways to use flow digest structures to update state changes, recover the connections after a failover, and solve the state inconsistency are presented. The main advantage of the proposed method is to reduce the bandwidth consumption on state replication. The simulation results show that the proposed scheme reduces the number of update messages and, more importantly, eliminates typically at least 86% of bandwidth consumption compared to current solutions.