分布式和云计算系统4-6章习题

Problem 4.2:

a. Virtualized data center

Virtualized 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 technology

Green 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 as

energy-efficient as possible, and designing algorithms and systems for

efficiency-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 technique

Multitenant 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 4.11

Advantages of using virtualized resources in cloud computing applications Resource management -

1.Service providers enjoy greatly simplified software installation, maintenance

and centralized control.

2.To efficiently access and manage resources to reduce operations and systems

management 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 enabling

dynamic sharing of resource pools.

Application flexibility -

1.Amazon EC2 is at one end of the spectrum. An EC2 instance looks much like

physical 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 platforms

such as Google AppEngine. AppEngine is targeted exclusively at traditional

web applications, enforcing an application structure of clean separation

between a stateless computation tier and a stateful storage tier. AppEngine

has impressive automatic scaling and high-availability mechanisms.

3.It can be used for interactive mobile applications, parallel batch processing, in

business analytics, as an extension to compute-intensive desktop applciations Cost - effectiveness -

1.The elimination of an up-front commitment by Cloud users, thereby allowing

companies to start small and increase hardware resources only when there is an increase in their needs.