Open Grid Services Architecture

1
Open Grid Services Architecture

• Maciej Malawski

2
Motivation

• Globus Toolkit new standard for scientific
  applications
• Web Services new standard in industry
• The Physiology of the Grid new paper by Foster,
  Kesselman
• Open Grid Services Architecture

3
Outline

• Web Services
• Protocols XML, SOAP, WSDL
• Example implementations
• Grid Services Open Grid Services Architecture
• Globus Toolkit 3.0

4
Web Services

• New standard middleware framework for performing
  system-to-system interaction
• Designed by industry (Microsoft, IBM, ...)
• Based on vendor-independent standards
• XML (eXtensible Markup Language)
• SOAP (Simple Object Access Protocol)
• WSDL (Web Services Definition Language)
• Interoperability

5
XML

• eXtensive Markup Language
• W3 Consortium standard
• Example
• ltgreetinggtHello, world!lt/greetinggt
• Many parsers in Java, C, C, Perl, etc. available

6
SOAP

• lightweight protocol to exchange information in a
  decentralized, distributed environment.
• XML based protocol that consists of
• an envelope that defines a framework for
  describing what is in a message and how to
  process it,
• a set of encoding rules for expressing instances
  of application-defined datatypes,
• a convention for representing remote procedure
  calls and responses (RPC)

7
Example of SOAP Request

• POST /StockQuote HTTP/1.1Host
  www.stockquoteserver.comContent-Type text/xml
  charset"utf-8"Content-Length nnnnSOAPAction
  "Some-URI"ltSOAP-ENVEnvelope  xmlnsSOAP-ENV"h
  ttp//schemas.xmlsoap.org/soap/envelope/"  SOAP-E
  NVencodingStyle"http//schemas.xmlsoap.org/soap/
  encoding/"gt   ltSOAP-ENVBodygt       ltmGetLastTr
  adePrice xmlnsm"Some-URI"gt           ltsymbolgtDI
  Slt/symbolgt       lt/mGetLastTradePricegt   lt/SOAP
  -ENVBodygtlt/SOAP-ENVEnvelopegt

8
Example of SOAP Response

• HTTP/1.1 200 OKContent-Type text/xml
  charset"utf-8"Content-Length
  nnnnltSOAP-ENVEnvelope  xmlnsSOAP-ENV"http//
  schemas.xmlsoap.org/soap/envelope/"  SOAP-ENVenc
  odingStyle"http//schemas.xmlsoap.org/soap/encodi
  ng/"/gt   ltSOAP-ENVBodygt       ltmGetLastTradePr
  iceResponse xmlnsm"Some-URI"gt           ltPricegt
  34.5lt/Pricegt       lt/mGetLastTradePriceResponsegt
     lt/SOAP-ENVBodygtlt/SOAP-ENVEnvelopegt

9
WSDL

• XML format
• To describe network services as a set of
  endpoints
• The operations and messages are described
  abstractly, and then bound to a concrete network
  protocol and message format to define an
  endpoint.
• Related concrete endpoints are combined into
  abstract endpoints (services).
• WSDL is extensible to allow description of
  endpoints and their messages regardless of what
  message formats or network protocols are used to
  communicate.

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WSDL Document

• Types a container for data type definitions
• Message an abstract, typed definition of the
  data being communicated.
• Operation an abstract description of an action
  supported
• Port Typean abstract set of operations supported
  by one or more endpoints.
• Binding a concrete protocol and data format
  specification for a particular port type.
• Port a single endpoint defined as a combination
  of a binding and a network address.
• Service a collection of related endpoints.

11
Other standards

• WSIL (Web Services Inspection Language) that
  enables publishing service descriptions
• UDDI (Universal Description, Discovery, and
  Integration) registry.
• accessible on the Web
• enable discovery of services that are advertised.

12
Implementations of Web Services

• Apache AXIS (Java)
• SOAPLite (Perl)
• gSOAP (C/C)
• Microsoft .NET
• Sun ONE
• ...

13
Apache AXIS

• Services run as Java Servlets
• Supports WSDL
• http//localhost8080/axis/services/MyService?WSDL
  
• WSDL2Java
• Stub classes for clients
• Skeleton classes for server
• Java2WSDL
• http//xml.apache.org/axis/

14
SOAPLite

• SOAP in Perl
• Client and server
• Easy to use
• use SOAPLite
• print SOAPLite
• -gt service('http//www.xmethods.net/sd/StockQuoteS
  ervice.wsdl')
• -gt getQuote('MSFT')
• http//www.soaplite.com

15
Open Grid Services Architecture

• Service orientation to virtualize resources
• From Web services
• Standard interface definition mechanisms
  multiple protocol bindings, multiple
  implementations, local/remote transparency
• Building on Globus Toolkit
• Grid service semantics for service interactions
• Management of transient instances ( state)
• Factory, Registry, Discovery, other services
• Reliable and secure transport
• Multiple hosting targets J2EE, .NET, C,

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OGSA Service Model

• System comprises (a typically few) persistent
  services (potentially many) transient services
• All services adhere to specified Grid service
  interfaces and behaviors
• Reliable invocation, lifetime management,
  discovery, authorization, notification,
  upgradeability, concurrency, manageability
• Interfaces for managing Grid service instances
• Factory, registry, discovery, lifetime, etc.
• gt Reliable, secure mgmt of distributed state

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The Grid Service

• A (potentially transient) Web service with
  specified interfaces behaviors, including
• Creation (Factory)
• Global naming (GSH) references (GSR)
• Lifetime management
• Registration Discovery
• Authorization
• Notification
• Concurrency
• Manageability

18
Factory

• A Grid service with Factory interface can be
  requested to create a new Grid service instance
• Reliable creation (once-and-only-once)
• Create operation can be extended to accept
  Grid-service-specific creation parameters
• Returns a Grid Service Handle (GSH)
• A globally unique URL
• Uniquely identifies the instance for all time
• Based on name of a home mapper service

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Mapper

• A GSH is a stable name for a Grid service, but
  does not allow client to actually communicate
  with the Grid service
• A Grid Service Reference (GSR) is a WSDL document
  that describes how to communicate with the Grid
  service (also CORBA IOR?)
• Contains protocol binding, network address,
• May expire (I.e. GSR information may change)
• The Mapper interface allows aclient to map from a
  GSH to a GSR
• http get on GSH also returns a GSR

20
Lifetime Management

• GS instances created by factory or manually
  destroyed explicitly or via soft state
• Negotiation of initial lifetime with Factory
• SoftStateDestruction interface supports
• GetTerminationTime message for inquiry
• Notification interface also allows for lifetime
  notification
• SetTerminationTime message for keepalive
• Soft state lifetime management avoids
• Explicit client teardown of complex state
• Resource leaks in hosting environments
• ExplicitDestruction interface also available

21
Registry

• The Registry interface may be used to discover a
  set of Grid service instances
• Returns a WS-Inspection document containing the
  GSHs of a set of Grid services
• Also returns policy associated with the set
• Also available through Discovery interface
• The RegistryManagement interface allows for
  soft-state registration of a Grid service
• A set of Grid services can periodically register
  their GSHs into a registry service, to allow for
  discovery of services in that set

22
Discovery

• A Grid service instance may maintain a set of
  service information
• XML fragments encapsulated in standard
• ltname, type, TTL-infogt containers
• Discovery interface allows clients to query the
  Grid service instance for this information
• Query operation, plus supporting operations
• Extensible query language support
• See also Notification interfaces
• Allows notification of service existence and
  about service information

23
Notification Interfaces

• NotificationSource for client subscription
• One or more notification generators
• Generates notification message of a specific type
• Typed interest statements E.g., Filters, topics,
  
• Supports messaging services, 3rd party filter
  services,
• Soft state subscription to a generator
• NotificationSink for asynchronous delivery of
  notification messages
• A wide variety of uses are possible
• E.g. Dynamic discovery/registry services,
  monitoring, application error notification,

24
Application Example (1-2)
25
Application Example (3-4)
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Use of Web Services

• Grid service interfaces defined in WSDL
• A GSR is a WSDL document (or may be something
  else, i.e. CORBA IOR)
• A GSH is an URL, with the following properties
• Globally unique for all time
• http get on GSH .wsdl returns GSR
• Can derive GSH to Mapper from it

27
Globus in OGSA

• GRAM Gatekeeper (Grid Resource Allocation and
  Management) Factory
• MDS (Meta Directory Service) Registry /
  Discovery
• GSI / TLS for protocol bindings
• GridFTP change control channel protocol

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Refactoring of protocols
29
Globus Toolkit 3.0

• Implemetation of OGSA
• To be available this year (Lee Liming)
• First implementation based on Apache AXIS (Java)
• SOAP HTTP TLS/GSI as protocols
• APIs remain the same