web and grid services
DESCRIPTION
Web and Grid Services. Slides taken from a variety of sources: GT4 tutorial, by Borja Sotomayor http://gdp.globus.org/gt4-tutorial/ International Summer school on Grid Computing 2007m by Malcolm Atkinson http://www.iceage-eu.org/issgc07/index.cfm HP introduction to WSRF by Sanjay Dahiya - PowerPoint PPT PresentationTRANSCRIPT
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Web and Grid Services
Slides taken from a variety of sources:GT4 tutorial, by Borja Sotomayorhttp://gdp.globus.org/gt4-tutorial/
International Summer school on Grid Computing 2007m by Malcolm Atkinson
http://www.iceage-eu.org/issgc07/index.cfm HP introduction to WSRF by Sanjay Dahiya
http://foss.in/slides/lb2004/wsrf-intro.ppt
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• Service Oriented Architecture• Web Services• WS-RF• Globus implementation of WS-RF• OGSA-DAI
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Service Oriented Architectures:Three Components
Registries
Service Consumers
Services
Register an available serviceSend name & description
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Three Components
Registries
Service Consumers
Services
Request a serviceSend a description
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Three Components
Registries
Service Consumers
Services
Set (possibly empty)of matching
services
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Three Components
Registries
Service Consumers
ServicesRequest service operation
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Three Components
Registries
Service Consumers
ServicesReturn result or Error
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Composed behaviour
• Services are themselves consumers– They may compose and wrap other services
• The registry is itself a consumer• A federation of registries may deal with registry
services reliability & performance• Observer services may report on quality of services
and help with diagnostics• Agreements between services may be set up
– Service-Level Agreements
– Permitting sustained interaction
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Web Services
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Web Services
• Enable communication between machines• Provide any number of functionality• Can be found and invoked• Self-describing—tell you how they can be invoked
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• Web Services are platform-independent and language-independent, since they use standard XML languages
• Most Web Services use HTTP for transmitting messages (such as the service request and response) – Good for going through firewalls
• Issues:– Overhead: XML is not as efficient for data transmission as using a
proprietary binary code. What you win in portability, you lose in efficiency.
– Limited in functionality, no explicit state management or lifecycle management
Web Services
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Typical Service Invocation
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The Web Services architecture
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A typical web service invocation
• Whenever a client needs to communicate with a service, it calls a client stub
• The client stub will turn this 'local invocation' into a proper SOAP request
• The SOAP request is sent over a network using the HTTP protocol. The server receives the SOAP requests and hands it to the server stub which invokes the service implementation
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Web Server• Web service: software that exposes
a set of operations
• SOAP engine: knows how to handle SOAP requests and responses--Apache Axis
• Application server: provides a space for applications that multiple clients can access—a container--Jakarta Tomcat server
• Http server: knows how to handle HTTP messages
Sometimes a container is described as: SOAP engine + application server + HTTP server
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Limitations of Web Services
• No explicit state management or lifecycle management
• Web services are usually stateless• Many services do
not need state
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Adding state to services
• Need to allow clients to access appropriate state
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“Stateless” vs. “Stateful” Services
• Without state, how does client:– Determine what happened (success/failure)?– Find out how many files completed?– Receive updates when interesting events arise?– Terminate a request?
• Few useful services are truly “stateless”, but WS interfaces alone do not provide built-in support for state
Client
FileTransferService
move (A to B)move
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Open Grid Services Architecture
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Before OGSA
• Grid services before OGSA– Resource management (Globus GRAM)
– Resource discovery (Globus MDS)
– Data Management (Globus GridFTP, RLS)
– Security
• All had – Different mechanism for access
– Different mechanism for discovery
– Different mechanisms for management
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OGSA
• Brings “order” to distributed services• Promotes “open” standards: defined in GGF (now OGF),
OASIS• Enables Virtualization
– Encapsulation behind a common interface of diverse implementations
• Allows the composition of lower-level services to form more sophisticated services
• Defines common behaviors that all services must have:– Naming– Lifetime management– State management– Notification
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WSRF
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FileTransferService (without WSRF)
• Developer reinvents wheel for each new service– Custom management and identification of state: transferID
– Custom operations to inspect state synchronously (whatHappen) and asynchronously (tellMeWhen)
– Custom lifetime operation (cancel)
Client
FileTransferService
move (A to B) : transferIDmove
statewhatHappen
tellMeWhen
cancel
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WSRF in a Nutshell• Service• State representation
– Resource– Resource Property
• State identification– Endpoint Reference
• State Interfaces– GetRP, QueryRPs,
GetMultipleRPs, SetRP
• Lifetime Interfaces– SetTerminationTime– ImmediateDestruction
• Notification Interfaces– Subscribe– Notify
• ServiceGroups
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
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FileTransferService (w/ WSRF)
• Developer specifies custom method to createResource and leaves the rest to WSRF standards:– State exposed as Resource + Resource Properties and identified by
Endpoint Reference (EPR)
– State inspected by standard interfaces (GetRP, QueryRPs)
– Lifetime management by standard interfaces (Destroy)
ClientFileTransferService
createResource (A to B) : EPRcreateResource
RPs
Transfer getRP
queryRPs
destroy
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Grid Infrastructure: Open Standards
Web services(WSDL, SOAP, WS-Security, WS-ReliableMessaging, …)
WS-Resource Framework & WS-Notification*(Resource identity, lifetime, inspection, subscription, …)
WS-Agreement(Agreement negotiation)
WS Distributed Management(Lifecycle, monitoring, …)
Applications of the framework(Compute, network, storage provisioning,
job reservation & submission, data management,application service QoS, …)
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WS-Resource Properties
• Each resource has a Resource Properties document.• Resource Properties document is referred in
service portType in WSDL.• Defined in XML schema.• Each element in the Resource Properties document
is a Resource Property (RP).• Resource properties can be queried using multiple
query dialects.• Independent of back-end implementation.
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Accessing Resource Properties
• Pull– Client can query the RP document, using query engines.
• GetResourceProperty• GetMultipleResourceProperties• QueryResourceProperties
• Push– Allows services to send changes in their resources’ RPs
to interested parties.• WS-Notification
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WS-Notification
• Subscriber indicates interest in a particular “Topic” by issuing a “subscribe” request
• Broker (intermediary) permits decoupling Publisher and Subscriber
• “Subscriptions” are WS-Resources• Publisher need NOT be a Web Service• Notification may be “triggered” by:
– WS Resource Property value changes– Other “situations”
• Broker examines current subscriptions • Brokers may
– “Transform” or “interpret” topics– Federate to provide scalability
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WS-Notification
• Characteristics of WS-Notification:– Web services integration of traditional enterprise
publish/subscribe messaging patterns• Composes with other Web services technologies• Facilitates integration between different messaging middleware
environments– Standardizes the role of Brokers, Publishers,
Subscribers and Consumers– Provides two forms of publish/subscribe:
direct publishing and brokered publishing– Standardizes Web service message exchanges for
publishing, subscribing and notification delivery– Defines XML model of Topics and TopicSpaces to
categorize and organize notification messsages
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WS-Resource Lifetime• Creating new resources.• Destroying old resources.
– Immediate destruction.– Scheduled destruction using termination time.
• Soft-state lifetime management– Lifetime extension.
• Example :– jobs in a batch submission system could be represented as
resources
– submitting a new job causes a new resource to be created
– when the job is completed, the resource is destroyed.
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WS-ServiceGroups
• Service groups maintain information about collection of services or resources.
• ServiceGroupRegistration– Add new members to group using WS invocation.
• Represent service groups as resources.• MembershipContentRules
– Imposes restrictions on services that can become part of service group like implementing an interface.
• WS-Notifications for service group changes.• For example – Resource registries etc
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WS-BaseFaults• XML based fault transmission.• Associated with an operation in WSDL.• Includes standard datatypes for transmitting webservice faults
– Originator, Timestamp etc..
Example :
<wsdl:portType name="pt">
<wsdl:operation name="op">
<!-- WSDL operation fault elements for each distinct fault -->
<wsdl:input … />
<wsdl:output … />
<wsdl:fault name=“aFault" message="tns:aFaultMessage"/>
<wsdl:fault name="BaseFault" message="wsbf:BaseFaultMessage"/>
</wsdl:operation>
</wsdl:portType>
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Globus Toolkit implementation of WSRF
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Data Mgmt
SecurityCommonRuntime
Execution Mgmt
Info Services
GridFTPAuthenticationAuthorization
ReliableFile
Transfer
Data Access& Integration
Grid ResourceAllocation &
ManagementIndex
CommunityAuthorization
DataReplication
CommunitySchedulingFramework
Delegation
ReplicaLocation
Trigger
Java Runtime
C Runtime
Python Runtime
WebMDS
WorkspaceManagement
Grid Telecontrol
Protocol
Globus Toolkit v4www.globus.org
CredentialMgmt
Globus Toolkit: Open Source Grid Infrastructure
Tools for building WSRF
services
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GT4 WS Core in a Nutshell
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
Implementation of WSRF: Resources,
EndpointReferences, ResourceProperties
Operation Providers: pre-build implementations of
WSRF operations
Notification implementation: Topics, TopicSet, Embedded
Notification Consumer service
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Service Container
GT4 WS Core in a Nutshell
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
Service Container: host multiple services in container; one JVM
process
…more details: based on AXIS service
container, processes SOAP messages
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Service Container
GT4 WS Core in a Nutshell
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
Secure Communication: Transport, Message,
Conversation (Transport demonstrates best
performance)
PIP
PDP
Configurable Security Policies: Policy Information
Points (PIPs), Policy Decision Points (PDP) -- chained
Example authorization PDPs: GridMap, SAML
implementations
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Service Container
GT4 WS Core in a Nutshell
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
PIP
PDP
WorkManager DB Conn Pool JNDI Directory
WorkManager: “thread pool”, site independent
“work” manager
Apache Database Connection Pool library
(JDBC “DataSource” implementation)
JNDI Directory: manages internal, shared objects
(ResourceHomes, WorkManager,
Configuration objects,…)
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Apache Tomcat
Service Container
GT4 WS Core in a Nutshell
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
RPs
Resource
ServiceGetRP
GetMultRPs
SetRP
QueryRPs
Subscribe
SetTermTime
Destroy
EPREPR
EPR
ResourceHome
PIP
PDP
WorkManager DB Conn Pool JNDI Directory
Deploy Service Container “standalone”
or within Apache Tomcat
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Relationship Between OGSA, GT4, WSRF & Web Services
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Dealing with Data OGSA-DAI
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OGSA-DAI
• An extensible framework
• accessed via web services
• that executes data-centric workflows
• involving heterogeneous data resources
• for the purposes of data access, integration, transformation and delivery within a Grid
• and is intended as a toolkit for building higher-level application-specific data services
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Motivation• Grid is about sharing resources
• OGSA-DAI is about sharing structured data resources
RelationalDatabase
XMLDatabase
IndexedFile
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Sharing data via website download
• ZIP up data and put it on a website• Pros
– Easy distribution for providers
– Easy access for consumers
• Cons– Consumers have to download all the data
– Consumers have to load data into local databases to use it
– Static snapshot
– Security
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Sharing data via direct access
• Providers tell consumers– Database URL – mycomputer.epcc.ed.ac.uk:3306– Username – userID – Password – password
• Pros– Consumers have direct access, so it should be faster
• Cons– Firewall issues– User and password management is hard– No consistent security model– Hard to use in grid/web service workflows– Continued on next slide…
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Sharing data via direct access
• Cons (continued)– No server-side layer in which to standardize database
heterogeneities
– Client needs to know, and have installed, correct driver for the database.
– Different drivers for Java, C#, C++, Fortran etc.
– Totally different API for different database types, e.g. JDBC for Relational, XMLDB for XML, Lucene for indexed files.
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• Manipulate data using domain-specific operations, e.g.– Book findByISBN(ISBN)
– List<Book> findByAuthor(Author)
– List<Book> findByKeyword(Word)
• Pros– Fits with grid/web service approach
– Abstraction hides back-end database details
– Web services are programming language neutral
– Operations likely to map well to authorization policies
Domain-specific web services
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• Cons– Slower than direct access
• Web service layer
• SOAP transport overhead – especially for large result sets
– Domain-specific API prevents use of generic data exploration, mining and manipulation tools
Books Cancer
UniversityEmployees
Generic Data LinkingApplication
Books writtenby Universityemployees
Universityemployees in
1932 who havesince died of
cancer
Domain-specific web services
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OGSA-DAI generic web services• Manipulate data using OGSA-DAI’s generic web services
• Clients sees the data in its ‘raw’ format, e.g.– Tables, columns, rows for relational data
– Collections, elements etc. for XML data
• Clients can obtain the schema of the data
• Clients send queries in appropriate query language, e.g. SQL, XPath
RelationalDatabase
XMLDatabase
IndexedFile
OGSA-DAI
request
data
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OGSA-DAI
• Pros:– Fits with grid/web service approach.
– Web services are programming language neutral.
– Access to schema and raw data supports generic tools.
• Cons:– Slower than direct connection mainly due to SOAP
overhead.
– One more layer between client and data
– Data not transferred in efficient binary format.
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Reducing the SOAP effect – workflows
TransformWeb Service
OGSA-DAI
FTP Server
OGSA-DAI
FTP Server
Query ->Transform ->DeliverToFTP