Ogsa ogsi service elements and layered model
- 1. Prof. Neeraj Bhargava Pooja Dixit Department of Computer Science School of Engineering & System Sciences MDS, University Ajmer, Rajasthan, India 1
- 2. There are two main logical components of OGSA: (i) the Web-services-plus- OGSI layer, and (ii) the OGSA-architected services layer. Four main layers comprise the OGSA architecture: 1. Grid applications layer. This layer is the user-visible layer. It supports user applications. Eventually, a “rich” set of grid-architected services is expected to be developed. 2. OGSA-architected grid services layer. Services in this layer include: Discovery, Lifecycle, State management, Service Groups, Factory, Notification, and Handle Map. These services are based on the Web services layer. The GGF was working at press time to define many of these architected grid services in areas such as program execution, data services, and core services. Some are already defined (and implementations have already appeared.) 3. Web Services layer, plus the OGSI extensions that define grid services. The OGSI specification defines grid services and builds on standard Web services technology. OGSI exploits the mechanisms of Web services such as XML and WSDL to specify standard interfaces, behaviors, and interaction for all grid resources. OGSI extends the definition of Web services to provide ca- pabilities for dynamic, stateful, and manageable Web services that are required to model the resources of the grid. 4. Physical and logical resources layer. Physical resources include servers, storage, and network. Above the physical resources are logical resources. Logical resources provide additional function by virtualizing and aggregating the resources in the physical layer. General-purpose middleware such as file systems, database managers, directories, and workflow managers provide these abstract services on top of the physical grid. 2
- 3. The structure of OGSA architected services. • grid-architected services divided into four categories, as shown in Figure : 1. Grid core services 2. Grid program execution services 3. Grid data services 4. Domain-specific services 3
- 4. Grid Core Services. It composed of four main types of services: 1. Service management 2. Service communication 3. Policy management 4. Security Service management. Service management provides functions that manage the services deployed in the distributed grid. It automates a variety of installation, maintenance, monitoring, and troubleshooting tasks within a grid system. Service management includes functions for provisioning and deploying the system compo nents; it also includes functions for collecting and exchanging data about the operation of the grid. This data is used for both “online” and “offline” management operations,and includes information about faults, events, problem determination, auditing, metering, accounting, and billing. Service communication. This includes a gamut of functions that support the basic methods for grid services to communicate with each other. These functions support several communication models that may be composed to enable effective inter service communication, including queued messages, publish–subscribe event notification, and reliable distributed logging. Policy services. These create a general framework for creation, administration, and management of policies and agreements for system operation. Policy services include policies governing security, resource allocation, and performance, as well as an infrastructure for “policy-aware” services to use policies to govern their operation. 4
- 5. Policy and agreement documents provide a mechanism for the representation and negotiation of terms between service providers and their clients (either user requests or other services); terms include specifications, requirements, and objectives for function, performance, and quality that the suppliers and consumers exchange and that they can then use to influence their interactions Security services. Security services support, integrate, and unify popular security models, mechanisms, protocols, and technologies in a way that enables a variety of systems to interoperate securely. These security services enable and extend core Web services security protocols and bindings and provide service-oriented mechanisms for authentication, authorization, trust policy enforcement, credential transformation, and so on. 5
- 7. An example grid service deployment and publishing diagram. 7
- 8. Grid program execution services and grid data services. 8
- 9. Grid Program Execution Services. It is depicted in Figure. Mechanisms for job scheduling and workload management implemented as part of this class of services are central to grid computing and the ability to virtualize processing resources. Although OGSI and core grid services are generally applicable to any distributed computing system, the grid program execution service class is unique to the grid model of distributed task execution that supports high-performance computing, parallelism, and distributed collaboration. Grid data services are also depicted in figure. These interfaces support the concept of data virtualization and provide mechanisms related to distributed access to information of many types including databases, files, documents, content stores, and application- generated streams. Domain-Specific Services. The three categories discussed above (grid core services, grid program execution services, and grid data services) represent areas of active work by GGF research or working groups. Over time, as these services mature, domain-specific services can also be specified. Domain-specific services will make use of the functionality that these services supply. It is critical that the GGF working groups are concentrating on specifying a broad set of useful grid services that software vendors and developers can then begin to implement. 9