With the rise of virtualization as a platform for hosted services provision, virtual appliances have come to provide a direct route for traditional on-premises applications to be rapidly redeployed in a software as a service (SaaS) mode – without requiring major application re-architecture for multi-tenancy. By decoupling the hardware and operating system infrastructure provider from the application stack provider, virtual appliances allow economies of scale on the one side to be leveraged by the economy of simplicity on the other. Traditional approaches to SaaS, such as that touted by Salesforce.com, leverage shared infrastructure by forcing massive change and increased complexity on the software stack.