Live migrations of virtual machines are required in cloud data centers in various contexts such as evacuating a host machine for maintenance, balancing the workloads on host machines, optimizing physical resource utilization, and meeting the custom demands of the user applications.Virtual machine migrations can, however, be costly in terms of both resources consumed for the migration as well as in terms of service level agreement (SLA) violations during the migration window. The cost is determined by many factors and they, in turn, are impacted by WHEN the migration happens during the lifetime of the virtual machine. Empirical studies show that if we have a window in which the migration is to be done (proactive rather than reactive where no such window exists), we can do it by carefully choosing the starting point within the window so that the SLA violation is minimum. In this paper, we propose a model to migrate virtual machines opportunistically to minimize the SLA violations. The idea is to find the time instants, called opportunities, at which, if the migration starts, the number and extent of SLA violations are minimal. Our experiments show that the migrations time savings with opportunistic migrations are up to 25%. KEYWORDS cloud computing, opportunistic live migration, virtual machines
INTRODUCTIONLive virtual machine (VM) migrations are performed in cloud data centers (CDC) for various reasons such as evacuating a host machine for maintenance, balancing the workloads on host machines, optimizing physical resource utilization, and meeting the custom demands of the user applications. 1 One of the most significant advantages of live migration is the fact that it facilitates proactive resource management and maintenance. There are two approaches for live VM migration, pre-copy and post-copy. Pre-copy is the most commonly used mode of migration and has two phases. In the iterative copy phase, memory pages are iteratively copied from the source machine to the destination, all without stopping the execution of the VM being migrated. In the stop-and-copy phase, which follows the execution of VM, is suspended at the source to transfer all pages dirtied during the final iteration of the iterative copy phase and also the hardware state associated with the VM. 2 The duration of the stop-and-copy phase is the downtime of the VM being migrated.The VM migrations may be for either proactive or reactive resource management in a data center. In reactive resource management, VMs are migrated when the need arises, whereas in proactive resource management, migrations are carried out well before the actual need arises. 3Proactive resource management using existing predictive analytics tools is shown to be suitable for multi-tenant data centers to address cases such as timely management of load spikes. 4 Furthermore, live VM migration can be adaptive or non-adaptive. In case of adaptive migration, the rate of transfer of pages is adjusted based on the page dirtying rate, whereas in non-adaptive technique, pages are migrated at...