Speculative TCP Connection Admission Using Connection Migration in Cluster-Based Servers

This paper presents speculative TCP connection admission, a mechanism for improving sub-optimal request distribution decisions in cluster-based servers. Overloaded server nodes in the cluster speculatively accept incoming requests only to offload them to less-loaded nodes. Speculative admission uses connection endpoint migration, a technique that allows server-side connection endpoints to be arbitrarily assigned to server nodes in the cluster. Speculative connection admission targets distributed load balancing policies at the back-end level that leverage request routing decisions taken outside the cluster. The mechanism has been implemented in the Linux kernel as part of a policy-based software architecture for request distribution. We have been able to show that speculative connection admission adds little overhead to the normal TCP processing, offsets load imbalances and accommodates higher request rates. That makes it suitable for an active role in request distribution in cluster-based servers.