Agility in Virtualized Utility Computing

Virtual machines have emerged as an attractive approach for utility computing platforms because applications running on VMs are fault- and security- isolated from each other, yet can share physical machines. An important property of a virtualized utility computing platform is how quickly it can react to changing demand. We refer to the capability of a utility computing platform to quickly reassign resources as the agility of the platform. We are targeting hosting utility provider environments where the entire platform is under the control of a single administrative domain and application instances often form application-level clusters. In this work, we examine resource reassignment mechanisms in these environments from the agility perspective and outline a new mechanism that exploits properties of a virtualized utility computing platform. This new mechanism employs ghost virtual machines (VMs), which participate in application clusters, but do not handle client requests until activated by the resource management system. We evaluate this, as well as other, mechanisms on a utility computing testbed. The results show that this ghost VM approach is superior to other approaches in its agility, and allows a new VM to be added to an existing application cluster in a few seconds with negligible overhead. This is a promising result as we develop resource management algorithms for a globally distributed utility computing platform.