The Open Grid Services Architecture

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The Open Grid Services Architecture
(Ian Foster, Carl Kesselman, and Steven Tuecke)

• 2004. 01. 28
• Kim, Chang Soon
• Super Computing Laboratory
• Dept. of Computer Science, Yonsei Univ.

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CONTENTS

• Service-Oriented Architecture
• Service-Oriented GRID Architecture
• An Example
• Web Services
• Open Grid Services Infrastructure
• OGSA Services and Schema
• Case Study Revisited
• Other Issues
• OGSA Implementations
• Future Directions

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Service-Oriented Arch.

• What is Service?
• An entity that provides some capability by
  exchanging messages
• Some features
• This defining achieve great flexibility
• In how services are implemented
• Where they may be located
• All entities are services
• Goal of OGSA design
• Reuse of behaviors
• Ease of composition of simpler behaviors

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Service-Oriented Arch.

• Examples
• Storage service
• Data transfer service
• Troubleshooting service
• IDL (interface definition language)
• WSDL (Web Services Description Language)
• Provide well-known names
• Well-defined IDL Simplify the manipulation and
  management of services
• Service discovery
• Service composition
• Specialization
• Interface extension

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Service-Oriented Grid Arch.

• OGSI
• Describing and discovering service attributes
• Creating service instances
• Managing service lifetime
• Managing groups of services
• Subscribing and delivering notifications
• OGSA services
• Web service that adheres to OGSI standard
• OGSA schemas
• Needs a common vocabularyfor describing objects

Current Web Service do not support these
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An Example
Storage monitor service
Implemented in a different way QoS
File Transferservice
client
Same interface
Storage Broker service
Compelete example
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Web Services

• Perspective of OGSA
• Web services standard of most interest is WSDL
• Advantages of Web Service Framework
• Registering and discovering interface definition
• For dynamic discovery and composition of services
  in heterogeneous env.
• Widespread adoption
• Is defining concerned with
• Service registry
• Security
• Policy
• Service orchestration

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WSDL

• WSDL definition comprises
• Service interface
• Implementation details

OO terms
ltwsdldefinitions xmlnstns
targetNamespacegt ltmessage
namegetFileRequestgt ltpart nameterm
typexsstring/gt lt/messagegt ltmessage
namegetFileResponsegt ltpart namevalue
typexsstring/gt lt/messagegt ltportType
nameStorateServicechangegt ltoperation
namegetFilegt ltinput messagegetFileReque
st/gt ltoutput messagegetFileResponse/gt
lt/operationgt lt/portTypegtlt/wsdldefinitionsgt
Define a message
Methodargument
interface
class
operation
method
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Additional Element

• ltservicegt
• Defines endpoint address
• ltbindinggt
• Specify the messaging protocol, data-encoding
  model, transport protocol
• Separation of interface from binding
• Multiple bindings for a single interface

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OGSI

• Provision of standard interfaces semantics for
  common service interactions
• Interoperable, reusable components
• Mechanisms
• Grid service descriptions and instances
• Service data
• Naming and name resolution
• Service life cycle
• Fault groups
• Service groups

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Grid service descriptions and Instances

• Grid service descriptions
• Consists of the WSDL that defines the Grid
  services interfaces and semantics
• Grid service instance
• Addressable, stateful, transient instantiation of
  descripton

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Service Data

• Definition
• For representing metadata and state data related
  to a service
• WSDL has no concept of service state
• So OGSI has defined WSDL extensions
• Declaration of visible state
• Standard operations for accessing that state
• SDEs (Service data elements)
• Each interface can specify 0 or more SDEs
• Combination of All SDEs ? logical XML document
• OGSI defines
• Standard operation for accessing an document
• Standard attributes
• Capacity, location, speed, free-space, and so on
• Utilization
• Introspection, discovery, and monitoring

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Accessing Service Data Elements

• Pull-mode
• Query a Grid service instances service data
• Query expression
• Require Simple by name
• Optional multiple condition (e.g. XPath or
  Xquery)
• Push-mode
• Delivery of service data elements
• Notification

Notification- Source
Notification- Subscription
Notification-Sink
keepalive
Lifetime management
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Service Data Element Schema

• Being defined within OGSA
• E.g.) Common management models

Logical resources
Physical resouces
disk
map
file system
IP
Abstract representation of phy. rsc.
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Naming

• Requirements
• Require not a fixed mapping
• Two-level naming scheme
• GSH (Grid service handle)
• Globally unique name for all time
• No-protocol specific, no instance-specific
• Encapsulated into a single abstraction(GSR)
• GSR (Grid service reference)
• Dependent of the underlying protocol binding
• Expiration time
• Handle resolution services (HandleResolver)

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Naming (cont)

• Migration based on
• Resource availability
• Locality of a client
• Client privilieges

Resolver(GSH)
Client
Handle resolver
timegt T
timelt T
GSR1
GSR2
Migrate at time T
Serviceinstance
Service instance
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Service Life Cycle

• Grid services distinction from web service
• Grid service is transient, created as part of
  operation of the infrastructure
• ? need the mechanisms about lifetime of a service

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Creating Transient Services Factories

• OGSI defines
• Extensible Factory interface
• Have common and simple cases
• Factory interface is responsible
• Creating the new service instance
• Handle resolution service
• Virtualization method of Factory interface
• Implemented directly by a hosting environment
• Delegating the request to other factory services
• Composing behaviors of multiple lower-level
  services? higher-level service instance

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Service Lifetime Management

• Problem in distributed system
• Components fail and messages may be lost
• A Service never see an expected explicit
  termination request
• Consume resources indefinitely
• Soft-state approach
• Instances are created with a specified lifetime
• When Lifetime expired
• Terminate instances and release resources
• Mechanism
• Negotiating an initial lifetime
• Factory selects an initial time
• Explicit termination
• Requesting a lifetime modification

? Robust termination and failure detection !!
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Fault model

• OGSI fault model
• Required elements
• Originating service and a time-stamp
• ogsiFaultType element

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Service Groups

• Definition
• Collection of service instances
• OGSI interfaces
• ServiceGroup
• ServiceGroupRegistration
• ServiceGroupEntry

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CONTENTS

• Service-Oriented Architecture
• Service-Oriented GRID Architecture
• An Example
• Web Services
• Open Grid Services Infrastructure
• OGSA Services and Schema
• Case Study Revisited
• Other Issues
• OGSA Implementations
• Future Directions

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OGSA Services and Schema

• Examples
• Service discovery
• Service management
• Monitoring
• Security
• Data access messaging
• Services not standards, but useful
  capabilities
• Core services
• Data and information services
• Resource and service management service

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Core Services

• Name resolution and discovery
• OGSI HandleResolver interface
• Discovery interface
• Querying mapping from semantic information to
  GSHs
• Security
• Policy
• Determine the method of action based on a set of
  conditions (particular context)
• Messaging, queuing, and logging
• Events
• Metering and accounting

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Data and Information Services

• Data naming and access
• Need for interfaces for naming and accessing data
• Replication
• Metadata and provenance
• Maintaining various forms of metadata

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Resource and Service Management

• Provisioning and resource management
• Required for negotiating SLAs
• Service orchestration
• DAGman and Chimera systems
• Transactions
• Assure that transactions have executed correctly
• Administration and deployment

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Case Study Revisited

• Components of the file transfer framework

Keep track of the services
Simple example
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Flow of File Transfer
STEP
1. Negotiation SLAs
2. Delivery Service
3. Monitoring Infrastructure
DataTransfer
Delivery Service
Initiate desired file transfer !!
client
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Negotiating SLAs

• Prior to initiating a transfer
• Need SLAs between the storage system and consumer

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Establishment of delivery service
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Monitoring Infrastructure
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Other Issues

• Different features from OO systems
• Not required inheritance
• Does not prescribe any particular development
  approach (e.g. language-specific)
• Service-Oriented Arch. are not without potential
  problems
• IDL may be
• Insufficient to express services and operations
• Hinder high-performance execution
• Limited in their capabilities
• OGSA may have overcome, but it will not be able
  to predict!!

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OGSA Implementations

• Principles
• Implementing the Grid service instance directly
  as an operating system process
• More specialized component model(such as J2EE)
• Many of behaviors are supported by the hosting
  env.

GridServiceImpl.
Little opportunity for reuse
Protocoltermination
GridServiceImpl.
Protocoltermination
Demarshaling/Decoding
GridServiceImpl.
Protocoltermination
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OGSA Implementations (cont)

• GT3
• Complete implementation of OGSI
• Discovery services, submission and monitoring of
  jobs,reliable file transfer
• other capabilities are being refactored to be
  OGSI compliant
• Data delivery, replica location, authorization
• Other OGSI impl.
• pyGlobus
• UNICORE

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Future Directions

• Service and tools
• Implementation
• Semantics
• Scalability

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Summary

• Everything is represented as a Grid Service
• Important merit of service-oriented model is
  virtualization
• GT3 supports existing GT APIs as well as WSDL
  interfaces
• Development of OGSA represents a natural
  evolution of Web Services