Research On The Key Technology Of WebGIS Cluster Based On Server Virtualization

The combination of GIS and Internet has expanded new fields and new channels of GIS, and promoted the application and extension of geographic spatial information dramatically, which not only makes it more convenient to share the spatial information cross-regionally and cross-industrially, but also makes it more rapidly to develop the popularization of geographic information. The rapid development of WebGIS has been pushed forward owing to the great enhancement of the computer hardware performance, the promotion of new frameworks and new algorisms in software field, and continuous improvement of GIS subject. The unceasing penetration of the WebGIS application has brought about some new problems and challenges, for instance:the large numbers of Internet users and the mass data of GIS have made GIS application under great performance pressure; since software development lags behind hardware development at present, the role that new hardware plays in promoting WebGIS performance has been limited; the traditional WebGIS software and development model couldn’t satisfy the demand of GIS rapid development.WebGIS cluster has inherited the characteristics of computer cluster, which ensure the stability of service and application, release the server pressure dramatically, and make it more convenient to extend. Load balancing strategies and algorithms are one of the key technologies of cluster. The improvement of algorism is essential to promote cluster performance and stability, which is also the research focus of various research fields including WebGIS. The server virtualization, which has provided new methods for cluster construction, can be used to establish virtual cluster based on different servers and PCs much easily. Many scholars and researchers from GIS industries have put forward new methods and models to establish virtual WebGIS despite the fact that they all have their own advantages and limitations.On the basis of the project supported by the national science and technology, this paper focuses on the WebGIS cluster application models and the key technology realization methods based on the server virtualization, lays emphasis on such important issues as WebGIS cluster model construction, virtual resource allocation technology, load balancing strategies and algorisms, and service and interface models and so on. On this basis, the structurally proper WebGIS cluster model has been designed; the dynamic allocation problem of virtual resource in cluster has been solved; the load balancing algorism according with the features of GIS application has been realized; and the simple and applicable WebGIS service and interface model has been designed.The details of this study are stated as follows:(1) In this study, the present research conditions and tendencies of the server virtualization, WebGIS and cluster technology have been analyzed, which concludes the advantages of virtualization and cluster in promoting hardware resource utilization rate, system performance and usability and so on. Therefore, it makes virtualization and cluster effective technical means in enhancing WebGIS cluster reliability and performance. At the same time, some problems and difficulties in virtualization and cluster development, such as performance loss and load scheduling and so forth, must be studied and solved.(2) This paper then studies the structure model of WebGIS virtualization cluster. On the basis of studying the features and realization technologies of server virtualization, virtualization technology has turned out to be an effective method to improve the utilization rate of the server hardware, especially that of the processor. Under the current circumstances that the micro server based on multi-core processor has gained rapid development, the cluster system built on cheap server can deal with computational density problems of high time-space complexity, and can also be applied in GIS field. Analysis and comparison have been made between the cluster structures developed differently by national and international mainstream GIS platform providers. A structure model of WebGIS cluster has been proposed in connection with server virtualization technology. This model constructs cluster with1:1:1mapping among the numbers of processor core, OS, and GIS service instance. It has been compared with the solution of singular physical server with multi GIS service instance by experimental tests.(3) This paper also studies the resource allocation technology of WebGIS virtualization cluster. By analyzing ordinary methods of virtual machine resource allocation and placement strategies of virtual machine, a dynamic allocation technology of recourse based on cluster load prediction has been proposed. The time series modeling of the medium and long term cluster load history has been realized. A set of meteorological data has been experimented to test and verify this modeling. Strategies and algorisms of the virtual machine placement timing have been designed on the basis of load prediction. The algorism of virtual machine placement target selection has been put forward based on the least first strategy. The above algorism procedure and false code have been described. The experimental scene based on allocation algorism has been designed and tested on meteorological application, and the allocation technology has been verified.(4) The load balancing algorism of WebGIS virtualization cluster has been studied too. The features of genetic algorism and its application to load balancing scheduling have been studied at first, which indicates that it is adaptable and robust in WebGIS load balancing scheduling. According to the particularity and complexity of GIS algorism and application, the GIS task model has been constructed as the basis for genetic coding of genetic algorism based on the task priority and execution time. The genetic algorism of load balancing, including the fitness function, genetic operator and control parameter, has been designed, and algorism procedure has been formed. At last the algorism has been inserted in the load balancing module of WebGIS cluster to be experimented and tested.(5) The service and interface model of WebGIS virtualization cluster has been studied further. On the basis of studying the problems of the spatial data sharing and service frameworks, the service and interface model of lightweight GIS cluster based on ROA and the cross-browser client model based on RIA have been put forward to solve the problems of heavy SOA structure and complicated data model, lowering the complexity of interface model so that the customers can use it at ease.(6) At last the service prototype system of WebGIS virtualization cluster has been studied. The WebGIS cluster prototype framework based on server virtualization technology has been designed and constructed. The analysis and description of this prototype have been made from the aspect of specific technology accomplishment. Certain application in meteorological industry has been studied and experimented in order to put WebGIS virtualization cluster prototype into practice, make performance tests and verify the feasibility and rationality of cluster prototype.