Reducing the Migration Times of Multiple VMs on WANs Using a Feedback Controller

Virtual machine (VM) migration is affected by network latency and throughput, which are highly fluctuating and unpredictable in wide-area networks (WANs). Hence, it is difficult to statically minimize the time required to transfer a large number of VMs across WAN. The goal of this work is to migrate as many VMs as possible during a given period of time and it is motivated by disaster recovery scenarios. One approach is to migrate a large number of VMs in parallel, but this leads to long migration times of each individual VM. Long migration times are problematic in catastrophic circumstances where resources are limited and can fail within a short period of time. Thus, it is important to shorten both the total time required to migrate multiple VMs and the migration time of individual VMs. Due to network performance fluctuations, the optimal number of parallel migrations changes over time. This work proposes a feedback-based controller that adapts to the number of parallel VM migrations in response to changes in a WAN. The controller implements an algorithm inspired by the TCP congestion avoidance algorithm in order to regulate the number of VMs in transit depending on the network conditions. Experiments using a prototype controller confirm that it is possible to control the migration of a set of VMs shortening both the total and individual migration times. The experiments show that the controller shortens the individual migration time by up to 5.7 fold compared to that of the static VM migrations where the number of parallel migrations does not change until all migrations are completed. The contributions of this work are 1) introducing migration strategies for multiple VMs on WANs and 2) proposing a hypervisor-independent controller that adapts to network bandwidth fluctuations in disaster scenarios.