基于可用性度量的分布式文件系统节点失效恢复算法

现有分布式文件系统中处理节点失效时采用的恢复策略耗费较多的带宽与磁盘空间资源,且影响系统的稳定性。通过研究分布式文件系统HDFS集群结构、数据块存储机制、节点与数据块状态之间的关系,定义了集群节点矩阵、节点状态矩阵、文件分块矩阵、数据块存储矩阵与数据块状态矩阵为度量数据块可用性建立了基础数据模型。在实现数据块可用性度量基础上,设计了基于可用性度量的节点失效恢复算法并分析了算法的性能。实验结果表明:新算法在保证系统中所有数据块可用性的前提下比原恢复策略减少了恢复所需带宽与磁盘资源,缩短了节点恢复时间,提高了系统稳定性。     

云平台中MySQL数据库高可用性的设计与实现

为解决OpenStack云平台中单个节点的MySQL数据库在面临高并发访问和海量数据增长的情况下存在可靠性低、存储扩展性差、单点瓶颈等问题,设计并实现一种以Ceph分布式文件系统为存储后端的高可用MySQL数据库集群系统。通过集群技术消除基于独立服务器的单点瓶颈问题,保障业务的可靠性和高可用性,设计一套优化模型提高故障切换效率,底层的Ceph分布式文件系统为数据存储提供扩展性和安全性。实验结果表明,该MySQL高可用集群可以实现存储的扩展和节点失效情况下的故障切换,该优化模型可以有效降低故障切换时间。     

基于状态转移图的虚拟集群节点可用性分析

针对虚拟集群节点的可用性评价,提出了一种基于状态转移图的虚拟集群节点可用性模型。首先,通过分析虚拟集群节点的部署方式和运行过程,确立了虚拟集群节点的5种生命周期状态,并阐明了5种生命周期状态之间的转移关系;然后,对于无备用节点和有备用节点两种情况下的虚拟集群节点,分别给出了相应的状态转移图,并建立了一系列的可用性模型。根据实际虚拟集群系统的运行日志,设定所提出的虚拟集群节点可用性模型的参数值,然后进行了多次数值模拟实验。实验结果表明,所提出的虚拟集群节点可用性模型的分析结果与实际可用性水平一致,能够正确地反映虚拟集群节点的可用性规律。     

热插拔提高可用性

系统的可用性,取决于MTBF(平均无故障时间)及MTTR(平均修复故障时间)。MTBF值越大,MTTR值越小,整个系统的可用性就越高。对于宝德来说,给用户提供高可用的服务器,降低用户系统的故障和恢复时间,一直是宝德追求的目标。为此,宝德在服务器的设计上,其主要部件均支持热插拔技术,如     

联想多点集群完善SAN

联想多点服务器集群系统是一个商用的企业级全光纤集群解决方案,它可以提供全面的可用性管理,把计划的和非计划的停机时间降到最低。该方案基于联想 SureFibre 光纤磁盘柜和万全系列服务器,提供多节点的集群服务。能够满足企业日益增长的数据量需求以及不断发展的全球电子商务模式对数据的不间断要求。它能够完善企业的 SAN 环境,既可以通过光纤直接连到磁盘阵列,也可以通过光纤交换机到“存储池”。方案功能该系统具有良好的扩展性,支持2～32个节点的集群服务器;支持Oracle,Sybase,Informix,SQL,Lotus,Exchange,ⅡS 数据库的代理程序,还将委托软件厂商合作开发新的支持其他应用的代理程序。可配置用于确定恢复故障切换的最优     

基于并行容错网的对等服务器集群的设计与实现

为了提高服务器系统的可靠性、可用性和性能,并改变目前非对称式服务器集群资源利用率低的状况,我们提出了一种新的服务器集群实现方案一基于并行容错网的对等服务器集群。在服务器集群的实现中,我们采用了软件集群的方法,设计实现了服务器集群管理层和并行容错通信层。     

一种改进的动态告警负载均衡算法

负载均衡通过将大量的并发访问请求转发到多个服务器分别进行处理,以提高web集群的整体吞吐量.现有的负载均衡算法存在着引用负载因素过少、负载计算过于复杂、节点的负载抖动现象过于严重等问题.本文提出一种改进的动态告警负载均衡算法,基于请求类型、节点工作能力和实时负载值来确定转发目标.该方案实时监测各节点的负载状态并实施周期性反馈与动态告警,既保证了负载信息的实时性与有效性,又减少了负载计算量;采用RED方法校正负载状态的判定,避免了因为负载状态的误判而引发的负载不均,从而减小了负载抖动现象.模拟实验结果表明,改进算法增加了web集群系统的吞吐量,并且明显改善了负载均衡度.     

故障Torus网络中的空闲子网搜索方案研究*

为了提高多处理机系统的抗故障能力,对现有的子网搜索算法进行改进,提出了一种新的基于故障节点模式的空闲子网搜索方案。以具有故障节点的二维Torus网络为例,详细阐述了方案的具体内容,并给出了相关的算法。该方案是基于集合操作的,能够显著缩小搜索范围并缩短比较时间。实例证明该方法具有可行性。     

基于分散式查找的Web服务器集群

随着www用户快速增加，人们对Web服务器的需求也越来越高，集群是解决这个问题的一种重要方案。但是现有的Web服务器集群还存在自适应性差、有系统瓶颈等不足。该文在分散式查找算法Pastry的基础之上，提出，一种新的Web服务器集群方案。它具有分散式查找算法的诸多优点，如可扩展、自组织、高容错和分散特性，较好地克服了传统Web服务器集群方案的不足。     

嵌入式Web集群服务器节能机制的研究与实现

提出一种针对嵌入式Web集群服务器的能耗节约机制,将其应用于基于Linux的嵌入式Web集群平台。分别探讨了集群平台的前端和后端服务器的节能方案：通过动态负载估算,在前端设计了控制后端服务器的开关算法,并在该算法中实现了阈值机制;后端服务器使用DVS策略,使之可根据负载情况动态调整处理器的工作频率。实验结果表明,和标准的Linux内核以及已有的节能方案相比,该方案节能效果显著。     

An SSL Back-End Forwarding Scheme in Cluster-Based Web Servers

State-of-the-art cluster-based data centers consisting of three tiers (Web server, application server, and database server) are being used to host complex Web services such as e-commerce applications. The application server handles dynamic and sensitive Web contents that need protection from eavesdropping, tampering, and forgery. Although the secure sockets layer (SSL) is the most popular protocol to provide a secure channel between a client and a cluster-based network server, its high overhead degrades the server performance considerably and, thus, affects the server scalability. Therefore, improving the performance of SSL-enabled network servers is critical for designing scalable and high-performance data centers. In this paper, we examine the impact of SSL offering and SSL-session-aware distribution in cluster-based network servers. We propose a back-end forwarding scheme, called ssl_with_bf, that employs a low-overhead user-level communication mechanism like virtual interface architecture (VIA) to achieve a good load balance among server nodes. We compare three distribution models for network servers, round robin (RR), ssl_with_session, and ssl_with_bf, through simulation. The experimental results with 16-node and 32-node cluster configurations show that, although the session reuse of ssl_with_session is critical to improve the performance of application servers, the proposed back-end forwarding scheme can further enhance the performance due to better load balancing. The ssl_with_bf scheme can minimize the average latency by about 40 percent and improve throughput across a variety of workloads.     

CoRAL: A transparent fault-tolerant web service

The Web is increasingly used for critical applications and services. We present a client-transparent mechanism, called CoRAL, that provides high reliability and availability for Web service. CoRAL provides fault tolerance even for requests being processed at the time of server failure. The scheme does not require deterministic servers and can thus handle dynamic content. CoRAL actively replicates the TCP connection state while maintaining logs of HTTP requests and replies. In the event of a primary server failure, active client connections fail over to a spare, where their processing continues seamlessly. We describe key aspects of the design and implementation as well as several performance optimizations. Measurements of system overhead, failover performance, and preliminary validation using fault injection are presented.     

A Tiered System for Serving Differentiated Content

Contemporary Web sites typically consist of front–end Web servers, application servers, and back-end information systems such as database servers. There has been limited research on how to provide overload control and service differentiation for the back-end systems. In this paper we propose an architecture called tiered service (TS) for these purposes. In TS, there are several heterogeneous back-end systems to serve the Web applications. The Web applications communicate with a routing intermediary to intelligently route the queries to the appropriate back-end servers based on various policies such as client profiles and server load. In our system the back ends may store different qualities of data; lower quality data typically requires less overhead to serve. The main contributions of this paper include (i) a tiered content replication scheme that replicates tiered qualities of data on heterogeneous back ends with different capacity to satisfy clients with diverse requirements for latency and quality of data, and (ii) an application-transparent query routing architecture that automatically routes the queries to the appropriate back ends. The architecture was implemented in our test bed, and its performance was benchmarked. The experimental results demonstrate that TS offers significant performance improvement.     

一种Web集群系统下的QoS控制策略

本文提出了一种在Web集群环境下的QoS控制策略。集群前端分配器以会话单位来分配访问请求,保证后端服务器间负载的合理均衡分配,同时后端服务器采用基于会话的QoS控制策略,实现对集群系统的服务质量控制。     

The implementation of a secure and pervasive multimodal Web system architecture

While most users currently access Web applications from Web browser interfaces, pervasive computing is emerging and offering new ways of accessing Internet applications from any device at any location, by utilizing various modes of interfaces to interact with their end users. The PC and its back-end servers remain important in a pervasive system, and the technology could involve new ways of interfacing with a PC and/or various types of gateways to back-end servers. In this research, cellular phone was used as the pervasive device for accessing an Internet application prototype, a multimodal Web system (MWS), through voice user interface technology.This paper describes how MWS was developed to provide a secure interactive voice channel using an Apache Web server, a voice server, and Java technology. Securing multimodal applications proves more challenging than securing traditional Internet applications. Various standards have been developed within a context of Java 2 Micro Edition (J2ME) platform to secure multimodal and wireless applications. In addition to covering these standards and their applicability to the MWS system implementation, this paper also shows that multimodal user-interface page can be generated by using XSLT stylesheet which transforms XML documents into various formats including XHTML, WML, and VoiceXML.     

基于机群的可扩展计算机网络系统构架

基于机群的可扩展计算机网络已逐渐成为高性能网络服务器架构的基础。文章对几种典型的机群构架进行了研究，包括RR-DNS—Web服务器 AFS服务器、TCP路由器 Web服务器、主-从服务器等，对它们的并行性问题，例如可扩展性、可靠性以及负载平衡策略等，作了深入的比较分析。     

Parallel failure recovery techniques in cluster-based media servers

For large-scale video-on-demand (VOD) service, cluster servers are highlighted due to their high performance and low cost. A cluster server consists of a front-end node and multiple backend nodes. Though the increase in backend nodes provides more quality of service (QoS) streams, the possibility of backend node failure is proportionally increased. The failure causes not only the cessation of streaming services but also the loss of current playing positions. In this paper, when a backend node fails, recovery mechanisms are studied to support the streaming service continuously. Without considering the characteristics of cluster-based servers and MPEG media, the basic redundant array of independent disks (RAID) techniques cause a network bottleneck in the internal network path and demonstrate inefficient CPU usage in backend nodes. To address these problems, a new failure recovery mechanism is proposed based on the pipeline computing concept. The proposed method not only distributes the internal network traffic generated from the recovery operations but also utilizes the CPU time available in the backend nodes. In the experiments, even if a backend node fails, the proposed method provides continuous streaming media services within a short MTTR value as well as more QoS streams than the existing method.     

基于互联网服务器的海量ZigBee节点管理系统

为解决海量ZigBee节点的组网与集中管理问题，文章提出一种基于互联网服务器的多ZigBee网络结构管理设计方案.系统将海量节点拆分为多个ZigBee网络结构，各个网络之间的设计不存在耦合，可摆脱无线传输的距离限制.每个独立的ZigBee网络中除终端节点与ZigBee协调器外，新增一个可接入互联网的控制器来组成内网结构.内网中的ZigBee节点利用Z-Stack协议栈实现自组网功能，控制器主要用于实现节点与服务器之间的通讯.文章提出中央服务器的概念作为外网结构的核心，用于维护中央数据库内所有节点的状态信息，同时对客户端提供Web服务.客户端对于系统内任意节点的查询或控制操作均由中央服务器代理完成.经测试表明系统运行可靠，扩展性强，具有一定参考价值.     

一种改进LKH的组播密钥管理方案

逻辑密钥树方案有效地减轻了组播通信中组成员及组控制器的负担,但组通信过程中的开销较大。提出了一种新的组播密钥管理方案,该方案根据组成员失效概率大小,将失效概率大的组成员置于右子树中右孩子节点处,而根节点和左孩子为相同组成员,从而构建逻辑密钥二叉树,这与现存LKH方案中密钥树的创建过程不同。通过对逻辑密钥二叉树的构造以及仿真实验的分析,均说明该方案在节点失效后的密钥更新量、节点的存储量比LKH方案要小,网络的抵抗性能好。     

基于关键网络状态的域内路由可用性研究

业界通常采用路由保护方案来提高域内路由可用性.然而已有的路由保护方案存在下面两个方面的问题:a)没有考虑网络中链路的失效概率,同等对待网络中所有的链路,事实上在互联网中,不同链路的失效概率是不同的,因此应该在路由保护方案中考虑链路的失效概率;b)将保护链路的数量作为设计目标,事实上方面某些链路出错的概率非常低,保护这些链路反而会增加开销,而另一方面某些链路出错的概率非常高,需要重点保护这些链路.因此应该将路由可用性作为路由保护方案的设计目标.针对上述两个问题,提出了一种基于关键网络状态的域内路由保护方案(RPBCNS),该算法首先通过链路失效概率计算出所有的关键网络状态,然后在每种关键网络状态下计算节点对之间相应的路径,保证节点对之间路径的多样性,从而使得尽可能多的节点对满足路由可用性需求.仿真实验将RPBCNS算法与主流算法ECMP、DC、path splicing分别在三个真实网络中进行对比,在网络可用性和节点对可用性满足率上RPBCNS的性能明显优于其他三种算法.仿真结果表明,RP-BCNS不仅具有较高的网络可用性,并且能够使得尽可能多的节点对满足路由可用性目标,更符合实时应用的实际需求.