Design And Implementation Of Cluster Communication System For Web Application Server

Web application server(WAS) provides a common infrastructure for the development, deployment, integration, running and maintenance of multi-tier distributed enterprise applications. With the increase of user number and data volume in network computing environment, a single WAS cannot always satisfy the need for performance and reliability. It is necessary to improve the availability, scalability and processing capability of WAS with clustering technology. Reliable cluster communication is the base of WAS information exchange. However, there still exist problems such as low adaptability, deficient fault tolerance and lack of configurability in most cluster communication systems of today's application servers. This thesis focuses on these problems and studies the design and implementation of web application server cluster communication system.Firstly, this thesis studies the key issues of maintaining the consistency and correctness of cluster structure. It analyzes the application requirements of WAS cluster structure and implements an adaptive dynamic topology. The consistency of topology views is kept around the cluster members and graceful joining and leaving operations are performed. This thesis brings about a distributed noncentral management mechanism to avoid performance and availability bottleneck. Homonymous clusters are detected through heartbeat signals and merged by automatic administrative server degradation to keep the uniqueness of clusters. A fail-detect chain is implemented to reorganize the cluster in a limited period of time in case that any number of servers would fail. And a new administrative server would be selected if the original failed, which greatly improves the whole availability of clusters.Secondly, this thesis studies three types of models of WAS cluster message transport: PUB/SUB model, constant peer-to-peer model and temporary peer-to-peer model. It implements the optimized multicast based on cluster cooperation and uses sliding windows to fulfill flow-control. Gossip algorithm is extended in the LAN environment to facilitatethe distributed message acknowledgement. Real-time update of dynamic topology view is used to prevent failed instances to block message transfer. Thus, reliable message exchange is implemented on top of unreliable multicast protocols.At last, this thesis describes the implementation of the flexibly configurable cluster communication system - CCSAS. In CCSAS, XML structural object model and Java dynamic binding mechanism are used to dynamically load instances of functionality class according to the component parameters and runtime policies, which grants the administrator of cluster capabilities of flexibly changing runtime rules such as cluster structure, backup policy and load balancing method. A cluster with great flexibility is achieved in this way.The CCSAS cluster communication system has been integrated in the J2EE web application server OnceAS which is developed independently by the Institute of Software, Chinese Academy of Sciences. Now OnceAS has been widely used in such fields as E-Government, E-Commerce and ERR...