Resilience of Cloud Computing in Critical Systems

With the increasing utilisation of Internet services and cloud computing by many organisations (both private and public), it is clear that computing is becoming the fifth utility (along with water, electricity, telephony and gas). These technologies are used for almost all types of systems, and critical systems are now no exception. Even if critical systems appear not to rely directly on cloud services, there may be hidden interdependencies that could affect their resilience. This paper investigates the uses of cloud computing in relation to critical systems and how this affects their resilience, initially comparing it with existing models and frameworks. Some examples are presented together with the associated risks. A framework is introduced for analysing the dependability and resilience of a system that relies on cloud services and how to improve them. As part of the framework, the concepts of micro and macro dependability are introduced to explain the internal and external dependability on services supplied by an external cloud. A pharmacovigilance model system has been used for framework validation.