Abstract
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Despite numerous improvements in the devel … Despite numerous improvements in the development and
maintenance of software, bugs and security holes exist in today’s
products, and malicious intrusions happen frequently.
While this is a general problem, it explicitly applies to webbased
services. However, Byzantine fault-tolerant (BFT)
replication and proactive recovery offer a powerful combination
to tolerate and overcome these kinds of faults,
thereby enabling long-term service provision. BFT replication
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 considered
unsuitable for web-based services.
In this paper we present SPARE, a cloud-aware approach
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 activating
up to f additional replicas by utilizing virtualization
in case of timing violations and faults. For an instant reaction,
we keep spare replicas that are periodically updated
in a paused state. In the fault-free case, these passive replicas
require far less resources than active replicas and aid
efficient proactive recovery. icas and aid
efficient proactive recovery.
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