分布式和云计算系统4-6章习题

Problem 4.2:a. Virtualized data centerVirtualized data center refers to data center that operates using virtualization technology. Servers, storage, and networks can all be virtualized through the use of system software and hardware virtualization techniques. From the user point of view, the user will not care about the computing resources that are used for providing the services. The users do not need to know and have no way to discover physical resources that are involved while processing a service request. And also, from the developer point of view, the application developers are not care about some infrastructure issues such as scalability, fault tolerant as they are virtualized.An example is Amazon Web Services (AWS), which provides elastic cloud computing service through the use of XEN hypervisor and virtual machines; provides storage cloud service though block store, augmented key/blob store, and automatic scaling varies from EBS to fully automatic; provides network cloud services through declarative IP level topology, elastic IP and so on.b. Green information technologyGreen IT refers to environmentally sustainable computing or IT. It is defined as the study and practice of designing, manufacturing, using, and disposing of computers, servers, and associated subsystems, such as monitors, printers, storage devices, and networking and communications systems, efficiently and effectively with minimal or no impact on the environment. The goals of green IT includes to reduce the use of hazardous materials, maximize energy efficiency during the product's lifetime, and promote the recyclability or biodegradability of defunct products and factory waste. Research continues into key areas such as making the use of computers asenergy-efficient as possible, and designing algorithms and systems forefficiency-related computer technologies.An example of green IT can be seen in EMC Corporation, who has been evolving its physical IT infrastructure into a private cloud in these years. For stored data, they have employed information lifecycle management, energy-efficient Flash drives, and archiving technologies that have shrunk the data footprint and relocated it to much more energy-efficient SATA drives. They use state-of-the-art reduplication technologies for backups and thin provisioning when allocating storage capacity to support business applications. They are also improving the power and cooling systems in the facilities to achieve further green computing.c. Multitenant techniqueMultitenant technique refers to a principle in software architecture where a single instance of the software runs on a server, serving multiple tenants. With a multitenant architecture, a software application is designed to virtually partition its data and configuration, and each client organization works with a customized virtual application instance. Therefore, it is one of the essential attributes of Cloud Computing.According to this understanding, basically Amazon Web Services (AWS), , Google App Engine, and Microsoft Azure are all examples of multitenant technique, as they all have multi-tenancy at some level in the system architecture stack.Problem 4.11Advantages of using virtualized resources in cloud computing applications Resource management -1.Service providers enjoy greatly simplified software installation, maintenanceand centralized control.2.To efficiently access and manage resources to reduce operations and systemsmanagement costs while maintaining needed capacity.e virtualization to have a single server function as multiple virtual servers.e virtualization to respond dynamically to the application needs of the users.e virtualization to increase the use of existing resources by enablingdynamic sharing of resource pools.Application flexibility -1.Amazon EC2 is at one end of the spectrum. An EC2 instance looks much likephysical hardware, and users can control nearly the entire software stack, from the kernel upwards. This low level makes it inherently difficult for Amazon to offer automatic scalability and failover, because the semantics associated with replication and other state management issues are highly application-dependent.2.At the other extreme of the spectrum are application domain specific platformssuch as Google AppEngine. AppEngine is targeted exclusively at traditionalweb applications, enforcing an application structure of clean separationbetween a stateless computation tier and a stateful storage tier. AppEnginehas impressive automatic scaling and high-availability mechanisms.3.It can be used for interactive mobile applications, parallel batch processing, inbusiness analytics, as an extension to compute-intensive desktop applciations Cost - effectiveness -1.The elimination of an up-front commitment by Cloud users, thereby allowingcompanies to start small and increase hardware resources only when there is an increase in their needs.2.The ability to pay for use of computing resources on a short-term basis asneeded (e.g., processors by the hour and storage by the day) and release them as needed, thereby rewarding conservation by letting machines and storage go when they are no longer useful.3.Applications for Microsoft’s Azure are written using the .NET libraries, andcompiled to the Common Language Runtime, a language-independent managed environment. Thus, Azure is intermediate between application frameworks like AppEngine and hardware virtual machines like EC2.Dependability -1.Increases the reliability of a single physical server when you have a certainnumber of virtual machines running on it.2.Recovery in case of failure of VM is fast.3.It has a good response to load induced failures.4.It can administer patches in an availability preserving manner.5.Enforcement of fail-safe behaviour.6.Intrusion detection and prevention.Problem 5.1:Differences between WS-* and RESTful Web services:On the transport layer, WS-* SOAP messages can be transported over various protocols such as, HTTP, SMTP, FTP, etc., while RESTful Web services can only run over HTTP. This limits the application scope of RESTful Web services.On the messaging layer, all messages in WS-* Web services are formatted as SOAP messages in XML, while the payload REST messages can be of various types, including HTML, plain text, JPEG, PDF, etc. As a result, SOAP messages are heavy-weight and resource-consuming to process, especially for non-text payloads. In the service and operation description layer, the WS-* Web services rely on WSDL to describe the set of operations supported by the services, and therefore, can support many different types of operations. In contrast, RESTful Web services only support 4 types of operations: PUT, GET, POST, and DELETE, and each REST message includes enough information to describe how to process the message.On the service publication and discovery layer, WS-* Web services rely on UDDI to register and discover services, while RESTful Web services are identified through URIs and can be bookmarked or exchanged via hyperlinks, without the need of a central registry such as UDDI.In terms of Quality of Service, WS-* Web services can support stateful services with different levels of QoS, while RESTful Web services are stateless and provide no QoS control.In terms of service composition, WS-* Web services are mainly applied in composition of business processes or workflows, while the composition of RESTful Web services has been the main focus of composite Web 2.0 application, such as “Mash-ups”. Amazon S3 supports communication using both standard SOAP and RESTful Web services, but REST is the preferred mechanism, due to the difficulties of processinglarge binary objects in the SOAP API and in particular, the limitation that SOAP puts the object size to be managed and processed.Problem 5.15:Why are Grids popular in academic applications while clouds dominate commercial use?∙Grid supports high performance computing and high throughput applications, which is subsidized by federal grants for the access by academia.∙Cloud is designed for on demand usage and pay as you go as a business model supported by industry∙Most of the time academic and commercial applications consist of different application types. Academic applications often require complex datacommunication and synchronization among the parallel components. Theseare often implemented using technologies like MPI and utilize highperformance hardware and networking support, which is provided by Grids.Commercial applications, which are often written in MapReduce liketechnologies and deployed on commodity hardware are not sensitive to suchnetwork latencies and do not depend on complex inter-processcommunication making them suitable for cloud environments.Problem. 6.12:.。