Future of grids resources management
5.4 Cloud services .1 Three-level services.1Three-level services
Generally, cloud computing can provide three-level services where the cus-tomers can choose one or more special service as they wish. For their special use, the customers can rent hardware, software or data as a service. There-after an integrated computing platform as a service is available. At the highest level, infrastructure used as a service is provided.
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FIGURE 5.2: Cloud protocol architecture.
• Hardware as a service (HaaS) / Software as a service (SaaS) / Data as a service (DaaS):
- Hardware as a service (HaaS) is a pay-as-you-go model for accessing a provider’s IT hardware, or even an entire data center. Some companies sell use of their hardware over the Internet on a per-use basis [Wang et al., 2008 ]. The user sends data and a program to process that data, while the vendor’s computer does the processing and returns the result.
The HaaS is flexible, scalable and manageable to meet the user’s needs.
An example is the IBM blue cloud project [IBM, 2007 ]. IBM delivers hardware infrastructure, database management, monitoring, security, availability and contingencies to be consumed by clients and partners directly.
- Software as a service (SaaS) is hosting software or application as a service and provided to customers across the Internet. This mode elim-inates the need to install and run the application on the customer’s local computers [Church et al., 2008 ]. SaaS therefore alleviates the customer’s burden of software maintenance, and reduces the expense of software purchases by on-demand pricing. An example of the SaaS is Microsoft’s software plus service, which combines local software and Internet services interacting with one another [Microsoft Corp., 2008 ].
- Data as a service (DaaS) is related to the fact that users can access remote data in various formats and from multiple sources. And then they operate them just like on a local disk. Typical example is Amazon simple storage service which provides a simple web services interface that can be used to store and retrieve, declared by Amazon, any amount of data, at any time, from anywhere on the web [Amazon Inc., 2008 ].
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• Platform as a service (PaaS): Based on the support of the HaaS, SaaS and DaaS, the cloud computing in addition can deliver the platform as a Service for users. Platform as a service (PaaS) offers a high-level integrated environment to build, test and deploy custom applications.
Generally, developers need to accept some restrictions on the type of software they can write in exchange for built-in application scalability.
Google’s App Engine enables users to build web applications on the same scalable systems that power Google applications [Google, 2008 ].
• IaaS: Infrastructure as a service (IaaS) provisions hardware, software and equipments to deliver software application environments with a re-source usage-based pricing model. Infrastructure can scale up and down dynamically based on application resource needs. Amazon proposed elastic cloud computing service [Amazon Inc., 2009 ] which uses the Eucalyptus’s open source cloud as the interface [Eucalyptus, 2009 ] to allow people to set up a cloud infrastructure at premise and experiment prior to buying commercial services.
Figure 5.3 shows the relationship between these services. Clouds provide services at three different levels. According to users’ special demands, they can not only subscribe to their favorite computing services with requirements of hardware configuration, software installation and data access, but also be supplied with the higher level environment, integrated platform or open in-frastructures.
5.4.2 Service characters
The services could be classified into several categories, as below:
• Dynamic provision: The provision of services is on-demand, which means that the users request the service by themselves near real-time without users having peak loads. Performance is monitored. Loosely-coupled architectures are constructed using web services as the system interface. At the same time, users can re-provision technological infras-tructure resources rapidly and inexpensively.
• Economic pricing: As a kind of consumed utility, the capital expendi-ture is greatly reduced and converted to operational expendiexpendi-ture. The infrastructure is typically provided by a third-party and does not need to be purchased for one-time or infrequent intensive computing tasks, so the users have easier entry to the computing world. Pricing on a util-ity computing basis is fine-grained with usage-based options and no IT skills are required for implementation. Cloud providers should mask this pricing granularity with long-term, fixed price agreements considering the customer’s convenience.
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FIGURE 5.3: Three-level services.
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• Security guarantee: Security typically improves due to centralization of data, increased security-focused resources, etc., but raises concerns about loss of control over certain sensitive data. Security is often as good as or better than traditional systems, in part because providers are able to devote resources to solve security issues that many customers cannot afford. Providers typically log accesses, but accessing the audit logs themselves might be difficult or impossible.
• Scalable location: In cloud computing, the users don’t know the exact position where the services and devices are offered. The independent attribute makes users access systems using a web browser regardless of their location or what device they are using. The third-party infrastruc-ture is accessed via the Internet; the users can connect from anywhere.
• Efficient utilization: The services in clouds can be compared as a large resource pool shared by users. The users not only can get lower costs because of the centralization of infrastructure, but also achieve higher peak-load capacity avoiding engineering for highest possible load-levels.
What’s more, through using the redundant sites, it’s easy for business continuity and disaster recovery.
• User/system interfaces: Browsers are used as user interface which have the attributes such as intuitive, easy-to-use, standards-based, service-independent and multi-platform supported [Gens, 2008 ]. System inter-face adopts web services APIs, which provide a standards-based frame-work for accessing and integrating with and among cloud services. Cloud services provide well-defined, programmed access for users, partners and others who want to leverage the cloud service within a broader solution context. Thus, the application software that provides web-based GUIs, web services APIs, multi-tenant architecture and a rich variety of con-figuration options should be well developed in the future.