开放网格服务架构：分布式系统整合的新视角

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"Grid架构的生理学：分布式系统集成的开放网格服务架构" 本文《Grid架构的生理学：分布式系统集成的开放网格服务架构》由Ian Foster、Carl Kesselman、Jeffrey M. Nick和Steven Tuecke撰写，深入探讨了如何通过开放网格服务架构（Open Grid Services Architecture, OGSA）解决在商业和科学领域中跨分布式、异构和动态的“虚拟组织”整合服务的问题。这些虚拟组织可能由单个企业内部的分散资源以及外部资源共享和服务提供商关系构成。首先，作者指出在这样的环境中进行服务集成的技术挑战主要在于，在不同原生平台之上运行时，需要确保各种服务质量（Quality of Service, QoS）。这包括但不限于性能、可靠性、安全性和可扩展性。 OGSA是一种基于网格和Web服务社区的概念和技术构建的解决方案。它提供了一种标准化的框架，允许不同系统之间的互操作性和资源的有效利用。该架构的核心是网格服务，它们是可发现、可组合和可控制的独立功能单元，可以在网格环境中提供服务。 1. **网格服务**：OGSA中的网格服务是实现跨域集成的关键组件。它们封装了特定的功能，并通过标准接口暴露服务，使得其他系统能够调用和利用这些服务。网格服务可以动态注册和注销，以适应不断变化的环境。 2. **中间件层**：OGSA中间件提供了必要的基础设施，支持网格服务的创建、发布、查找、绑定和执行。这包括服务注册与发现机制、事务管理、安全性、计费和QoS管理等。 3. **服务级别协议（Service Level Agreements, SLAs）**：为了确保不同平台间的服务质量，OGSA采用SLAs来定义和管理服务的预期性能和可用性。SLAs允许服务提供者和消费者之间明确地约定服务的条款和条件。 4. **网格信息服务中心（Grid Information Services, GIS）**：GIS是OGSA的重要组成部分，它维护网格中服务和资源的元数据，帮助服务消费者找到所需的服务，同时协助服务提供者进行资源调度和管理。 5. **安全模型**：OGSA考虑了分布式环境中的安全问题，提供了一套全面的安全模型，包括认证、授权、审计和隐私保护，以确保数据和服务的安全交互。 6. **可扩展性和互操作性**：OGSA设计的目标之一是支持大规模的可扩展性，能够处理数量庞大的服务和资源。同时，通过遵循开放标准和协议，OGSA提高了不同系统之间的互操作性。 7. **动态性与自适应性**：在OGSA中，系统能够根据需求和环境的变化动态调整，服务可以自我修复和自我优化，以保持整体系统的高效运行。通过OGSA，开发者和管理员可以构建灵活、可扩展且适应性强的网格环境，从而更好地整合和利用分布在全球各地的计算、存储和信息资源。这一架构为商业和科研领域的合作提供了强大支撑，降低了跨组织协作的复杂性。

Physiology of the Grid 6

Enterprises must then reintegrate (with QoS) these distributed servers and data resources,

addressing issues of navigation, distributed security, and content distribution inside the enterprise,

much as on external networks.

In parallel with these developments, enterprises are engaging ever more aggressively in e-

business and are realizing that a highly robust IT infrastructure is required to handle the

associated unpredictability and rapid growth. Enterprises are also now expanding the scope and

scale of their enterprise resource planning projects as they try to provide better integration with

customer relationship management, integrated supply chain, and existing core systems. These

developments are adding to the significant pressures on the enterprise IT infrastructure.

The aggregate effect is that qualities of service traditionally associated with mainframe host-

centric computing [56] are now essential to the effective conduct of e-business across distributed

compute resources, inside as well as outside the enterprise. For example, enterprises must

provide consistent response times to customers, despite workloads with significant deviations

between average and peak utilization. Thus, they require flexible resource allocation in

accordance with workload demands and priorities. Enterprises must also provide a secure and

reliable environment for distributed transactions flowing across a collection of dissimilar servers,

must deliver continuous availability as seen by end-users, and must support disaster recovery for

business workflow across a distributed network of application and data servers. Yet the current

paradigm for delivering QoS to applications via the vertical integration of platform-specific

components and services just does not work in today’s distributed environment: the

decomposition of monolithic IT infrastructures is not consistent with the delivery of QoS through

vertical integration of services on a given platform. Nor are distributed resource management

capabilities effective, being limited by their proprietary nature, inaccessibility to platform

resources, and inconsistencies between similar resources across a distributed environment.

The result of these trends is that IT systems integrators take on the burden of re-integrating

distributed compute resources with respect to overall QoS. However, without appropriate

infrastructure tools, the management of distributed computing workflow becomes increasingly

labor-intensive, complex, and fragile as platform-specific operations staff watch for “fires” in

overall availability and performance and verbally collaborate on corrective actions across

different platforms. This situation is not scalable, cost-effective, or tenable in the face of changes

to the computing environment and application portfolio.

2.2 Service Providers and Business-to-Business Computing

Another key trend is the emergence of service providers (SPs) of various types, such as web-

hosting SPs, content distribution SPs, applications SPs, and storage SPs. By exploiting economies

of scale, SPs aim to take standard e-business processes, such as creation of a web-portal presence,

and provide them to multiple customers with superior price/performance. Even traditional

enterprises with their own IT infrastructures are offloading such processes because they are

viewed as commodity functions.

Such emerging “eUtilities” (a term used to refer to service providers offering continuous, on-

demand access) are beginning to offer a model for carrier-grade IT resource delivery through

metered usage and subscription services. Unlike the computing services companies of the past,

which tended to provide offline batch-oriented processes, resources provided by eUtilities are

often tightly integrated with of enterprise computing infrastructures and used for business

processes that span both in-house and outsourced resources. Thus, a price of exploiting the

economies of scale that are enabled by eUtility structures is a further decomposition and

distribution of enterprise computing functions. EUtilities providers face their own technical

challenges. To achieve economies of scale, eUtility providers require server infrastructures that

can be easily customized on demand to meet specific customer needs. Thus, there is a demand for

This is a DRAFT document and a work in progress. Version: 6/22/2002.

Comments to foster@mcs.anl.gov, carl@isi.edu, jnick@us.ibm.com, tuecke@mcs.anl.gov

Physiology of the Grid 7

IT infrastructure that (1) supports dynamic resource allocation in accordance with service-level

agreement policies, efficient sharing and reuse of IT infrastructure at high utilization levels, and

distributed security from edge of network to application and data servers and (2) delivers

consistent response times and high levels of availability—which in turn drives a need for end-to-

end performance monitoring and real-time reconfiguration.

Still another key IT industry trend is cross-enterprise business-to-business (B2B) collaboration

such as multi-organization supply chain management, virtual web malls, and electronic market

auctions. B2B relationships are, in effect, virtual organizations, as defined above—albeit with

particularly stringent requirements for security, auditability, availability, service level

agreements, and complex transaction processing flows. Thus, B2B computing represents another

source of demand for distributed systems integration, characterized by often large differences

among the information technologies deployed within different organizations.

3 Background

We review two technologies on which we build to define the Open Grid Services Architecture:

the Globus Toolkit, which has been widely adopted as a Grid technology solution for scientific

and technical computing, and Web services, which have emerged as a popular standards-based

framework for accessing network applications.

3.1 The Globus Toolkit

The Globus Toolkit [29, 34] is a community-based, open-architecture, open-source set of services

and software libraries that support Grids and Grid applications. The toolkit addresses issues of

security, information discovery, resource management, data management, communication, fault

detection, and portability. Globus Toolkit mechanisms are in use at hundreds of sites and by

dozens of major Grid projects worldwide.

The toolkit components that are most relevant to OGSA are the Grid Resource Allocation and

Management (GRAM) protocol and its “gatekeeper” service, which provides for secure, reliable,

service creation and management [25]; the Meta Directory Service (MDS-2) [24], which provides

for information discovery through soft state registration [59, 69], data modeling, and a local

registry (“GRAM reporter” [25]); and the Grid Security Infrastructure (GSI), which supports

single sign on, delegation, and credential mapping. As illustrated in Figure 1, these components

provide the essential elements of a service-oriented architecture, but with less generality than is

achieved in OGSA.

Gatekeeper

(factory)

Reporter

(registry +

discovery)

User

process #2

User

process #1

Grid

Information

Index Server

(discovery)

User

Proxy Proxy #2

Other service

(e.g.,

GridFTP)

Authenticate &

create proxy

credential

Request

process

creation

Create

process

Contact

other

service

Figure 1: Selected Globus Toolkit mechanisms, showing initial creation of a proxy credential and

subsequent authenticated requests to a remote gatekeeper service, resulting in the creation of user

process #2, with associated (potentially restricted) proxy credential, followed by a request to another

remote service. Also shown is soft-state service registration via MDS-2.

This is a DRAFT document and a work in progress. Version: 6/22/2002.

Comments to foster@mcs.anl.gov, carl@isi.edu, jnick@us.ibm.com, tuecke@mcs.anl.gov

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开放网格服务架构：分布式系统整合的新视角

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