Unavailability-Aware Shared Virtual Backup Allocation for Middleboxes: A Queueing Approach

Network function virtualization provides an efficient and flexible way to implement network functions deployed in middleboxes as software running on commodity servers. However, it brings challenges for network management, one of which is how to manage the unavailability of middleboxes. This article proposes an unavailability-aware backup allocation model with the shared protection to minimize the maximum unavailability among functions. The shared protection allows multiple functions to share the backup resources, which leads to a complicated recovery mechanism and makes unavailability estimation difficult. We develop an analytical approach based on the queueing theory to compute the middlebox unavailability for a given backup allocation. The heterogeneous failure, repair, recovery, and waiting procedures of functions and backup servers, which lead to several different states for each function and for the whole system, are considered in the queueing approach. We analyze the performance bounds for a given solution and for the optimal objective value. Based on the developed analytical approach and the performance bounds, we introduce two heuristics to solve the backup allocation problem. The results reveal that, compared to a baseline model, the proposed unavailability-aware model reduces the maximum unavailability 16% in average in our examined scenarios.