SPARE: Replicas on Hold.
Tobias Distler, Ivan Popov, Wolfgang Schröder‐Preikschat, Hans P. Reiser, Rüdiger Kapitza · 2011
Despite numerous improvements in the development and maintenance of software, bugs and security holes exist in to-day’s products, and malicious intrusions happen frequently. While this is a general problem, it explicitly applies to web-based services. However, Byzantine fault-tolerant (BFT) replication and proactive recovery offer a powerful com-bination to tolerate and overcome these kinds of faults, thereby enabling long-term service provision. BFT replica-tion is commonly associated with the overhead of 3f + 1 replicas to handle f faults. Using a trusted component, some previous systems were able to reduce the resource cost to 2f +1 replicas. In general, adding support for proactive recovery further increases the resource demand. We believe this enormous resource demand is one of the key reasons why BFT replication is not commonly applied and consid-ered unsuitable for web-based services. In this paper we present SPARE, a cloud-aware ap-proach that harnesses virtualization to reduce the resource demand of BFT replication and to provide efficient support for proactive recovery. In SPARE, we focus on the main source of software bugs and intrusions; that is, the services and their associated execution environments. This approach enables us to restrict replication and request execution to only f + 1 replicas in the fault-free case while rapidly acti-vating up to f additional replicas by utilizing virtualization in case of timing violations and faults. For an instant reac-tion, we keep spare replicas that are periodically updated in a paused state. In the fault-free case, these passive repli-cas require far less resources than active replicas and aid efficient proactive recovery. 1.