OGSA : Open Grid Services Architecture

1. OGSA : Open Grid Services Architecture

2. Introduction • Developed by the Global Grid Forum • Aims to define a common, standard, open architecture for Grid Applications. • Defines a set of rules that make up a grid service. • Sharing and Coordinated use of diverse resources in Dynamic VO's

3. OGSA Framework-Background • Two Technologies to build OGSA: • Globus Tool Kit Community based Open Architecture, open set of services and software libraries that support Grids and Grid applications. • Web Services Popular Standards based framework for accessing network applications.

4. Web Service Standards.... • Web Services Description Language(WSDL)‏ • Standardized XML Format for describing network services. • Simple Object Access Protocol(SOAP)‏ • Messaging between service provider and requester.

5. Grid Services and OGSA • Web services with improved characteristics and services- Grid services • Provides a set of well defined interfaces and conventions. • Interface Addresses: a) Discovery, dynamic Service Creation. b) Lifetime Management, notification. • Conventions include: a) Naming Services b) Upgrade ability.

6. OGSA • OGSA defines the semantics of a Grid Service instance. • Defines the basic behavior and does not specify what a service does and how it does it. • Doesn't address issues of implementation programming model, language, tools and execution environment.

7. OGSA Technical Details • The OGSA Service Model: • Basic Premise: Everything is represented by a grid service. • Uniform Service Oriented Model • Specifies a core set of consistent interfaces from which all Grids are implemented. • Grid Services maintain internal state for the lifetime of the service.

8. Grid Service Interface • OGSA does not define a specific set of services • but defines a set of interfaces for manipulating service models. • A mandatory interface must be supported by all Grid services. • Interface for manipulating the grid service, handles the reference abstractions that define the OGSA model.

9. Grid Service Handle • Every Grid Service instance is assigned a globally unique GSH. • GSH carries no protocol specific or instance specific information. • All the instance specific information are encapsulated in a single abstraction called a Grid Service reference(GSR).

10. Grid Service Reference(GSR)‏ • Unlike GSH(time invariant), GSRs change during the service's lifetime. • GSR has an explicit expiration time. • OGSA employs a “Handle resolution ” mechanism for mapping GSH to GSR • OGSA mappings define mechanisms for obtaining an updated GSR.

11. Grid service migration • Mechanism for creating new services and specifying assertion regarding lifetime of a service. • The service that implements this interface is called a factory. • CreateService() operation creates a requested service and returns the GSH and an initial GSR. • Any service created must address the former services as the reference of later services.

12. Lifetime Management • Soft state approach: Every instance is created with a specific lifetime. • Initial lifetime can be extended by explicit client request. • Client can always know when the Grid Service will terminate. • Resource consumption at hosting environment is always bounded.

13. Notification • OGSA notification Framework allows clients to be notified by messages. • Interface also includes framework for asynchronous one way delivery of notifications. • The Source must support the OGSA notificationsource interface. • Clients wishing to receive notifications must implement notificationsink interface.

14. OGSA Security Models Grid work in heterogeneous environment which is open to public. We must be able to detect intrusion or stop viruses from spreading by implementing secure conversations, single logon, access control. Fig:OGSA security model implemented at various protection levels

15. Motivations for Standardization standards are critical to make the computing utility concept a reality. On the other hand, a corporate user just looking to securebetter utilization of its platforms and internal resources could start with a vendor-based solution and then move up to a standards-based solution in due course. Some specific areas where a lack of grid standards limit deployment are : Data management. Dispatch management. Information services. Scheduling Security. Work unit management.

16. Standard APIs enable application portability; • without standard APIs, application portability is difficult to accomplish (different platforms access protocols in different ways). • Standards enable cross-site interoperability; • Without standard protocols, interoperability is difficult to achieve. • Standards also enable the deployment of a shared infrastructure . • Use of the OGSI standard,provides the following benefits : • Increased effective computing capacity • Interoperability of resources • Speed of application development

17. Functionality Requirements • The development of the OGSA document has been based on a variety of use case scenarios. The use cases have not been defined with a view to expressing formal requirements but have provided useful input to the definition process. • The case scenarios that have been considered include: • National fusion collaboration, IT infrastructure and management,Commercial data centers,Service-based distributed query processing, Severe storm prediction, Online media and entertainment • Basic Functionality Requirements • Security Requirements • Resource Management Requirements • System Properties Requirements • Other Functionality Requirements

18. Basic Functionality Requirements Discovery and brokering • Mechanisms are required for discovering and/or allocating services, data, and resources with desired properties. • For example, clients need to discover network services before they are used, service brokers need to discover hardware and software availability, and service brokers must identify codes and platforms suitable for execution requested by the client Metering and accounting. • Applications and schemas for metering, auditing,and billing for IT infrastructure and management use cases . • The metering function records the usage and duration, especially metering the usage of licenses. • The auditing function audits usage and application profiles on machines, and the billing function bills the user based on metering Data sharing. Data sharing and data management are common as well as important grid applications. Mechanisms are required for accessing and managing data archives, for caching data and managing its consistency, and for indexing and discovering data and metadata.

19. Deployment. • Data is deployed to the hosting environment that will execute the job (or made available in or via a high-performance infrastructure). • Also,applications(executable) are migrated to the computer that will execute them. Virtual organizations (VOs). • The need to support collaborative VOs introduces a need for mechanisms to support VO creation and management • Depending on the customer’s request,thegrid will negotiate with another grid on a remote commercial data center and create a VO across the commercial data centers. • Such a VO can be used to achieve the necessary scalability and availability. Monitoring. • A global, cross-organizational view of resources and assets for project and fiscal planning, troubleshooting, and other purposes. • The users want to monitor their applications running on the grid. • Also, the resource or service owners need to surface certain states so that the user of those resources or services may manage the usage using the state information.

20. Policy. An error and event policy guides self-controlling management, including failover and provisioning. It is important to be able to represent policy at multiple stages in hierarchical systems, There may be policies at every level of the infrastructure: from low-level policies that govern how the resources are monitored and managed, to high-level policies that govern how business process such as billing are managed. High-level policies are sometimes decomposable into lower-level policies.

21. Security Requirements • Multiple security infrastructures Distributed operation implies a need to interoperate with and manage multiple security infrastructures. • Perimeter security solutions • Many users require applications to be deployed on the other side of firewalls from the intended user clients. • Intergrid collaboration often requires crossing institutional firewalls. • OGSA needs standard, secure mechanisms that can be deployed to protect institutions while also enabling cross-firewall interaction • Authentication, Authorization, and Accounting. • Obtaining application programs and deploying them into a grid system may require authentication/authorization. • Encryption. • The IT infrastructure and management users requires encrypting of the communications

22. Application and Network-Level Firewalls • This is a long-standing problem; • It is made particularly difficult by many different policies- one is dealing with and the particularly harsh restrictions at international sites • Certification • A trusted party certifies that a particular service has certain semantic behavior. • For example, a company could establish a policy of only using e-commerce services certified by Yahoo.

23. Resource Management Requirements • Resource management is another multilevel requirement, encompassing SLA negotiation, provisioning, and scheduling for a variety of resource types and activities: • Provisioning. Computer processors, applications, licenses, storage, networks, and instruments are all grid resources that require provisioning. • OGSA needs a framework that allows resource provisioning to be done in a uniform, consistent manner. • Resource virtualization. Dynamic provisioning implies a need for resource virtualization mechanisms that allow resources to be transitioned flexibly to different tasks as required; • for example, when bringing more Web servers on line as demand exceeds a threshold. • Optimization of resource usage while meeting cost targets (i.e., dealing with finite resources). Mechanisms to manage conflicting demands from various organizations, groups, projects, and users and implement a fair sharing of resources and access to the grid. • Transport management. For applications that require some form of real-time scheduling, it can be important to be able to schedule or provision bandwidth dynamically for data transfers or in support of the other data sharing applications. • Access. Usage models that provide for both batch and interactive access to resources.

24. Management and monitoring. • Management and monitoring of resource usage and the detection of SLA or contract violations by all relevant parties. • Also, conflict management is necessary; it resolves conflicts between management disciplines that may differ in their optimization objectives • Processor scavenging is an important tool that allows an enterprise or VO to use to aggregate computing power that would otherwise go to waste. • How can OGSA provide service infrastructure that will allow the creation of applications that use scavenged cycles? • For example, consider a collection of desktop computers running software that supports integration into processing and/or storage pools managed via systems such as Condor, Entropia, and United Devices. Issues here include maximizing security in the absence of strong trust. • Scheduling of service tasks. Long recognized as an important capability for any information processing system, scheduling becomes extremely important and difficult for distributed grid systems • Load balancing. In many applications, it is necessary to make sure deadlines are met or resources are used uniformly. These are both forms of load balancing that must be made possible by the underlying infrastructure. • Advanced reservation. This functionality may be required in order to execute the application on reserved resources

25. Notification and messaging. Notification and messaging are critical in most dynamic scientific problems. Notification and messaging are event driven. • Logging. It may be desirable to log processes such as obtaining/deploying application programs because, for example, the information might be used for accounting. This functionality is represented as “metering and accounting.” • Workflow management. Many applications can be wrapped in scripts or processes that require licenses and other resources from multiple sources. • Applications coordinate using the file system based on events. • Pricing.Mechanisms for determining how to render appropriate bills to users of a grid.

26. System Properties Requirements • Fault tolerance. Support is required for failover, load redistribution, and other techniques used to achieve fault tolerance. • Disaster recovery. Disaster recovery is a critical capability for complex distributed grid infrastructures. • Self-healing capabilities of resources, services and systems are required. Significant manual effort should not be required to monitor, diagnose, and repair faults. There is a need for the ability to integrate intelligent self-aware hardware such as disks, networking devices, and so on. • Strong monitoring for defects, intrusions, and other problems. Ability to migrate attacks away from critical areas. • Legacy application management. Legacy applications are those that cannot be changed, but they are too valuable to give up or to complex to rewrite. Grid infrastructure has to be built around them so that they can continue to be used. • Administration. Be able to “codify” and “automate” the normal practices used to administer the environment. The goal is that systems should be able to self organize and self-describe to manage low-level configuration details based on higher-level configurations and management policies specified by administrators. • Agreement-based interaction. Some initiatives require agreement-based interactions capable of specifying and enacting agreements between clients and servers (not necessarily human) and then composing those agreements into higher-level end-user structures.

27. Grouping/aggregation of services. The ability to instantiate (compose) services using some set of existing services is a key requirement. There are two main types of composition techniques: selection and aggregation. • Selection involves choosing to use a particular service among many services with the same operational interface. • Aggregation involves orchestrating a functional flow (workflow) between services. • For example, the output of an accounting service is fed into the rating service to produce billing records. One other basic function required for aggregation services is to transform the syntax and/or semantics of data or interfaces.

28. Other Functionality Requirements • Platforms. The platforms themselves are heterogeneous, including a variety of operating systems (Unixes, Linux, Windows, and, presumably, embedded systems), hosting environments (J2EE, .NET, others), and devices (computers, instruments, sensors, storage systems, databases, networks, etc.). • Mechanisms. Grid software can need to interoperate with a variety of distinct implementation mechanisms for core functions such as security. • Administrative environments. Geographically distributed environments often feature varied usage, management, and administration policies (including policies applied by legislation) that need to be honored and managed. • Both single-process and multiprocess (both local and distributed) applications covering a wide range of resource requirements. • Flows, that is, multiple interacting applications that can be treated as a single transient service instance working on behalf of a client or set of clients. • Workloadscomprising potentially large numbers of applications with a number of characteristics just listed.

29. Data-Intensive Grid Service Models • Applications in the grid are normally grouped into two categories: computation-intensive and data intensive. • For data-intensive applications, - deal with massive amounts of data. • For example, the data produced annually by a Large Hadron Collider may exceed several petabytes (1015 bytes). • The grid system must be specially designed to discover, transfer, and manipulate these massive data sets. • Transferring massive data sets is a time-consuming task. • Efficient data management demands low-cost storage and high-speed data movement. • Several common methods for solving data movement problems. • Data Replication and Unified Namespace • Grid Data Access Models • Monadic model • Hierarchical model • Federation model • Hybrid model • Parallel versus Striped Data Transfers

30. Data Replication and Unified Namespace • This data access method is also known as caching, which is often applied to enhance data efficiency in a grid environment. • By replicating the same data blocks and scattering them in multiple regions of a grid, users can access the same data with locality of references. • However, data replication may demand periodic consistency checks. • Replication strategies determine when and where to create a replica of the data. • The factors to be consider include data demand, network conditions, and transfer cost. • The strategies of replication can be classified into method types: dynamic and static. • static method, the locations and number of replicas are determined in advance and will not be modified. static strategies cannot adapt to changes in demand, bandwidth,and storage viability. • Dynamic strategies can adjust locations and number of data replicas according to changes in conditions (e.g., user behavior).

31. Grid Data Access Models • Multiple participants may want to share the same data collection. • To retrieve any piece of data, we need a grid with a unique global namespace. Similarly, we desire to have unique file names. • To achieve this, we have to resolve inconsistencies among multiple data objects bearing the same name. • Access restrictions may be imposed to avoid confusion. • Also, data needs to be protected to avoid leakage and damage. • Users who want to access data have to be authenticated first and then authorized for access. • In general, there are four access models for organizing a data grid, • Monadic model: This is a centralized data repository model, • All the data is saved in a central data repository. • When users want to access some data they have to submit requests directly to the central repository. • No data is replicated for preserving data locality. • This model is the simplest to implement for a small grid.

32. Hierarchical model: is suitable for building a large data grid which has only one large data access directory. • The data may be transferred from the source to a second-level center. • Then some data in the regional center is transferred to the third-level center. • After being forwarded several times, specific data objects are accessed directly by users. • PKI security services are easier to implement. • Federation model: is better suited for designing a data grid with multiple sources of data supplies.->also known as a mesh model. • The data sources are distributed to many different locations. • Although the data is shared, the data items are still owned and controlled by their original owners. • Hybrid model: This model combines the best features of the hierarchical and mesh models.

34. Parallel versus Striped Data Transfers • Parallel data transfer opens multiple data streams for passing subdivided segments of a file simultaneously. • Although the speed of each stream is the same as in sequential streaming, the total time to move data in all streams can be significantly reduced compared to FTP transfer. • In striped data transfer, a data object is partitioned into a number of sections, and each section is placed in an individual site in a data grid. • When a user requests this piece of data, a data stream is created for each site, and all the sections of data objects are transferred simultaneously. • Striped data transfer can utilize the bandwidths of multiple sites more efficiently to speed up data transfer.

35. Grid Services and OGSA • The OGSA , developed within the OGSA Working Group of the Global Grid Forum (recently renamed to Open Grid Forum or OGF and being merged with the Enterprise Grid Alliance or EGA in June 2006), • OGSA is a service-oriented architecture that aims to define a common, standard, and open architecture for grid-based applications. • “Open” refers to both the process to develop standards and the standards themselves. • In OGSA->everything from registries, to computational tasks, to data resources is considered a service. • OGSA is intended to: • Facilitate use and management of resources across distributed, heterogeneous environments • Deliver seamless QoS • Define open, published interfaces in order to provide interoperability of diverse resources • Exploit industry-standard integration technologies • Develop standards that achieve interoperability • Integrate, virtualize, and manage services and resources in a distributed, heterogeneous environment • Deliver functionality as loosely coupled, interacting services aligned with industry-accepted web service standards

36. ” OGSA gives a high-level architectural view of grid services and doesn’t go into much detail when describing grid services. • It basically outlines what a grid service should have. • A grid service implements one or more interfaces, where each interface defines a set of operations that are invoked by exchanging a defined sequence of messages, based on the Open Grid Services Infrastructure (OGSI) . • OGSI, also developed by the Global Grid Forum, gives a formal and technical specification of a grid service. • The interfaces address discovery, dynamic service creation, lifetime management, notification, and manageability; whereas the conventions address naming and upgradeability. • OGSA services fall into 7 broad areas,

37. • Infrastructure Services Refer to a set of common functionalities, such as naming, typically required by higher level services. • • Execution Management Services  starting and managing tasks, including placement, provisioning, and life-cycle management. • Tasks may range from simple jobs to complex workflows or composite services. • • Data Management Services Provide functionality to move data to where it is needed, maintain replicated copies, run queries and updates, and transform data into new formats. • These services must handle issues such as data consistency, persistency, and integrity. • The 3 base interfaces, Data Access, Data Factory, and Data Management, define basic operations for representing, accessing, creating, and managing data. • Resource Management Services Provide management capabilities for grid resources

38. • Security Services Facilitate the enforcement of security-related policies within a (virtual) organization, and supports safe resource sharing. • Authentication, authorization, and integrity assurance are essential functionalities provided by these services. • • Information Services Provide efficient production of, and access to, information about the grid and its constituent resources. • Self-Management Services Support service-level attainment for a set of services (or resources), with as much automation as possible, to reduce the costs and complexity of managing the system.