For security and auditability, Infrastructure as a Service (IaaS) providers isolate their tenants at a very low level as physical or virtual compute nodes. Individual tenants own and manage their compute nodes, software stack, networks and disks within an IaaS cloud. Typically, scale-out cloud applications run across a set of compute nodes solely dedicated to that application. In such an environment, three of the major objectives that general purpose operating systems were designed to meet are relaxed or eliminated entirely. First, the burden to support multiple users is removed from the operating system. In this environment, the isolation enforced by the IaaS provider eliminates the need for many system level security checks and accounting, and reduces the requirement for internal barriers between trusted and untrusted code. Second, it becomes the responsibility of the IaaS provider to arbitrate and balance competitive resource usage. In a deployment where entire nodes are assigned to a single application, much of the complexity of existing operating systems (e.g., scheduling, memory management, etc.) is redundant. Third, a symmetric structure is unnecessary in a large-scale distributed application. Many cloud applications are already composed of multiple services run across a set of compute nodes; As a result, OS functionality can be provided asymmetrically, where only some nodes need full OS functionality, while other nodes can be much simpler. Given these observations, it is apparent that distributed cloud applications built on top of general purpose systems are comprised of unnecessary software functionality with the risk of reduced performance and added complexity
