| Virtual machine technology was first put forward in the 60s of last century, when development appears in the IBM mainframe. With the further development of technology, the virtual machine (such as Xen, VMware) and virtual network (such as, VIOLIN, VNET, ViNe) has become the focus area in both the industry and academia. Virtual machine technology is designed to further improve the utilization of physical resources safely and effectively, to support multiple independent virtual machines(which is also known as client operating system, called VM as followed) running over one operating system, to shield heterogeneous underlying hardware, to achieve disaster protection and tolerance intrusion protection, to deploy a virtual cluster dynamically, to assist software testing, to meet different computing resources need for customization. And, it also has great potential for engaging in cloud computing and grid computing. Among these virtual techniques, live migration is one of the core research areas. Based on the good separation between underlying hardware and system software and unified lower interface, live migration technology could migrate from one host to another seamlessly and transparently, to facilitate fault management, load balancing, and data centers and virtual fleet management. Also, the migration of the operating system is opposed to process-level checkpoint migration technology. It's not strictly bound by the platform consistency. At the same time, many details of live migration technology also presented a larger challenge to the research.However, the representative of the live migration technology, there is Xen's Live Migration and VMware's VMotion, etc., they require VM migrating among those virtual machine hosts in the same LAN. This is a strict limit on flexibility and scalability of the virtual computing resources. At the same time, VM downtime is uncertainty during the migration steps when the time period of data packet may lose. The loss of data may result in the failure of communication-intensive tasks. Moreover, agents are used by the existing technologies to establish and maintain communication without changing anymore after initializing. This method is over-reliance on the original host and lacks of flexibility. So, how live-migration could be expanded to a multi-LAN environment and WAN effectively, and how to ensure reliable communications within migrating is very important. Objectives of this paper are also here.Our work is basing on Xen virtual machine platform to conduct a deep study of live migration processes and implementations of virtual machine and a clear mechanism of migration theory, and we have defined several the critical incident during the migration phases. Secondly, basing on the existing typical virtual network technology, we have learned the advantages of existing work to design an overlay layer of logical virtual network, in order to ensure the feasibility of inter-network communication when a virtual machine migrating across the networks. Again, basing on Virtual Routing in Virtual Networks and communication agents in VPN, we created an agent which could making direct connection with tunnels to ensure the data forwarding between networks efficiently. Finally, basing on virtual network routing protocols of my teammate, we could combine her work with the virtual network to ultimate a hybrid virtual network prototype.With the in-depth analysis of reason why the existing technology can not support virtual machine of Xen to migrate across the LAN, we have designed the virtual network architecture basing on the overlay layer. This overlay could meet the volatile demand of VM migrating, could create and revoke the agent process dynamically with sufficient using of resources; the efficiency of the whole virtual network could be enhanced with hybrid network architecture; the direct connecting tunnels between agents could make sure that data packages and command information transmitting exactly. More important, aiming at the problem of data loss in course of live migrating, we put forward an innovative distributed asynchronous cache protocol. This protocol coupling with caching mechanism could ensure the communication data without losing in live migration of virtual machine; we make full use of the advantages of the distributed cache to reduce dependence on the data-intensive storage; with advantage of asynchronous messaging mechanism, the normal data communication could be transparent with control message transmitting, and thus to keep the overall live migration of virtual machines reliably, orderly.Through a series of feasibility analysis and experimental demonstration, we could get the following conclusions as: the virtual network our designed could meet dynamic changes of virtual network topology with distinct flexibility; to solve the issue of communication between agents with dedicated tunnel, to make sure that networks can effectively realizing the data transmission; data cache the agreement could meet the demand of live-migration ,and could take advantage of live migration of the key events and control all the various modules to work together timely and accurate; capture module which is basing on filtering rules could obtain and forward accurate data; buffer module could distinguish between different virtual communications and capture and send stored data packets timely and accurately; the host or other virtual cluster address conflicts could be avoided and good isolation among them by the virtual IP address mechanism; hybrid network structure could reduce overhead of the virtual machine communication in the same network without forwarding by the tunnel.Our work of study the live migration mechanism is obvious of crucial significant, and we have get several innovation points, such as, distributed asynchronous cache protocol could solve data packet loss issues during migrating in WAN; to create and revoke communications agent is to separate from original network with dynamic characters; hybrid network structure of the virtual network to enhance the overall communication efficiency; virtual IP address isolate communication between virtual clusters, and assign to resolve a potential conflict.In all, this paper was designed and implemented basing on Xen virtual machine platform and given a hybrid prototype which count on the overlay layer of virtual network to support virtual machines across local area network communication; using a hybrid communications architecture that can enhance the efficiency of the virtual cluster communication; with a distributed asynchronous cache agreement, to resolve the data packet loss issues during the virtual machine live migration of the downtime period, and to ensure that the virtual machine communication reliability and orderliness. This work successfully achieved the virtual machine live migration across LANs and made a good job for the following study of live migration of virtual machines. Therefore, this study has far-reaching significance of scientific research. |
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