Web Services Based Architecture in
Computational Web Portals
Choonhan Youn cyoun@ecs.syr.edu
Department of Electrical Engineering and Computer Science Syracuse University
Presentation Outline
•
Introduction
– Grids
– What is the Computational web portal? – Limitations of traditional approach
•
Architecture of a Web Service based Computing Portal
– Standard services, interfaces, and protocols – Consequences of Web service architecture
•
Areas of research
– How to break up services into Web Services ==> Core Web services and Application Web services
– Integration of Security into Web Services – Data Service for the Earthquake simulation – Web services negotiation
•
Application: Interacting Data Services for Distributed
Earthquake Modeling
Grids Concept
• The basic Grid concept is based on coordinated resource sharing and problem solving in dynamic, multi-institutional Virtual Organizations.
– From I. Foster (ANL) in Globus: Technical paper
• Grid software enables loosely coupled, globally distributed computing. • What does that really mean?
– Specific services such as global authentication, resource allocation management, aggregated information services
– Centered around a few wire protocols and service implementations
• OGSI/OGSA
– Define mechanisms for creating, managing, and exchanging information among entities called Grid Services, building on both Grid and Web services technologies.
Grid Computing Environments
(GCE)
• GCEs are a general name for both Grid clients and middleware. • GCEs aim to bridge the gap between users and Grid infrastructure
developers.
• Organizations setting up Grids have seen the value of developing user environments, or Grid Computing Environments.
– 28 articles in November-December 2002 issue of Concurrency and Computation: Practice and Experience
– IPG Launchpad, HotPage, Alliance Portal, and others
• World-wide development community interacts through the GCE research group in the Global Grid Forum.
– G. Fox (IU), D. Gannon (IU), and M. Thomas (TACC) co-chair
• Grid portal technology is coming of age.
– Reusability of components
Computational Web Portals
• Computational Web Portals provide seamless access to HPC resources
– You can log in anywhere through any general web browser.
• Portals simplify the use of HPCs for novice users.
– Basics: batch script generation, job submission and monitoring, file service and ……
– Computational grid services: Globus, Condor
• Portals can simplify the use of unfamiliar codes.
– GEM code: disloc, simplex, GeoFEST, Virtual California, RIVA, …
• Provide a work management environment for all users.
– You can see what you did last week.
• Other PSEs/Web portals
– NASA IPG (Information Power Grid) LaunchPad
– NPACI Hotpage
– Pacific Northwest National Laboratory’s Ecce (Extensible Computational Chemistry Environment) system
Problems with Traditional Portal Architecture
• Portals accesses heterogeneous back ends and grids through a particular middle tier.
• Most portal projects are not interoperable
– Middle tier software incompatible – Wide range of protocols.
• Why do we need the portal interoperability?
– Portal developers avoid reinventing
every single important service (lesson from GGF GCE).
– Users will have access to more
services than any one project can provide and interact with someone else’s services.
services
Web browser Web browser
services
?
…
What will be our approach for solving the
interoperability problem?
• What is interoperability?
– In a network environment, interoperability means common protocols to which portal groups need to agree.
• General approaches.
– Bridge-based: services using different protocols.
• Immediate bridging • Mediated bridging
– Direct (universal protocols): all services using the same protocol.
• Web services provides universal protocol approach and are part of a broad industry and academic initiative to build distributed computing infrastructure around existing standards (HTTP, XML, etc).
• Basic components
– A common, simple wire protocol such as SOAP that most portals can agree to use and that can be delivered using standard wire protocols such as HTTP.
– A common format, that is, service description language such as WSDL for describing services provided.
– A common interface to information services such as a service registry UDDI or
WSIL that portals obtain information about which service providers have what kinds of services.
• A standard definition mechanism, standard lookup services, and standard transport definitions via SOAP.
Architecture of a Web Service based
Computing Portal - 1
•
Based on problems in the previous slide, we define a new
service-oriented architecture for computing portals.
– Distributed service model: The point of view that we take is that all back end resources should be considered as distributed services.
– Resource and service description: The generalized view of resources as services requires that we describe the metadata associated with the service and provide a means of locating and using it. WSDL is appropriate service description language.
– Resource and service discovery: Once we have described our service, it must be placed in an XML repository that can be searched by client, UDDI or WSIL as service discovery.
Architecture of a Web Service based
Computing Portal - 2
JS:Job submission
JM:Job Monitoring
FT:File Transfer
CM:Context Manager
SG:Script Generation
AWS:Application Web Service
HIS:Host Independent Service
HSS:Host Specific Service
Backend Resources Middle Tier (Web Server) Simulation Component JS JM FT HPC SOAP Data Component FT JS JM Data Base
… Web Services Provider
Service Repository Publish Publish SOAP SOAP SOAP SOAP CM SG AWS Middle Tier (Web Server) SOAP SOAP
User Interface Server
SOAP
Client RepositoryClient
SOAP HSS
HSS
Shortcomings of Web Service Model
•
Primitive services must be designed properly.
– Interfaces must be simple for external users – Implementation must be self-contained
•
Must extend Web Service to provide security.
– Message-level security infrastructure
•
Must combine primitive services into useful application
services.
– Application management service
•
Must extend Web Service to provide quality of service for
service compatibility.
Problems Defining Web Services for
Computing Portals
•
Standard interface and standard wire protocol
XML languages are not enough.
•
Web Service will still fail if particular service
interfaces are not designed properly.
•
Examples of this:
–
Gateway’s Context Manager class itself has 60(?)
methods. But, this does not make it externally useful.
–
Lessons learned from Batch Script Generation service
exercise we performed with SDSC.
How to break up services into Web Services
•
Services can be complicated but need to be self
contained, have a simple interface, should only
communicate with XML.
•
Services are separated from user interface.
–
Everything runs on a different server.
•
User interface itself can be distributed.
–
Define user interface web services (session state
management).
•
Services can be composite and selectable for
Proposal of Work: Web Service Design
•
Will define basic computing services and their
WSDL interfaces.
–
What are basic computing services?
v Job submission.
v File transfer and manipulation.
v Context manager( State information management ).
v Batch script generation service.
v Job monitoring service.
•
Need to come up with best practice design
patterns for distributed web services.
•
These basic services will be combined to create
Computing Portal Web Services
• We have built a suite of general purpose Grid Web services for managing distributed applications.
• Given WSDL and SOAP, what can you build?
• Core Computing services define general purpose functions:
– Host-Specific Services (HSS)
• Instances of these services are bound to particular hosts. • Job Submission
• File Transfer
• Job & Host Monitoring
– Host-Independent Services (HIS)
• Informational services that are not tied to specific service points • The service provided does not depend on the location.
• Context Management • Script Generation
• Application Web services include metadata about applications.
– Built on top of core services.
Core Web services - 1
•
Job Submission
– Allow users to execute scientific applications
– Execute operating system calls directly or may interact with Grid services through, for example, the CoG client API to Globus.
– We use Java Runtime processes to run external (non-Java) commands, for example, PBS qsub.
•
File Manipulation
– Upload and download files between their desktops and various backend destinations.
– Allow users to transparently move, rename, and copy files on remote back-ends and crossload between different backend sites.
– File uploading and downloading service illustrate the use of SOAP messages with attachments in the RPC messaging style.
Core Web services - 2
• Context Management (CM)
– Archives interactions with the computational portal and stores all of the metadata associated with user sessions.
– Provides simplest possible data model
• CM provides an easy interface to an arbitrarily deep and complex tree-shaped data structure. • Context data nodes are defined by recursive
schema that hold optional, unbounded name/value pairs and child nodes.
– We use CM to store locations of job scripts, miscellaneous file URIs, user’s application instance XML files, etc.
– CM metadata stored on file systems, XML-native databases, ….
• Actual data may be anywhere.
– Actual service interface for manipulating contexts and the context data
• Add one or more contexts.
• Search and store the context data with XPath queries.
Core Web services - 3
• Script Generation
– For users who are unfamiliar with HPC systems. – Generate the job script which could be broken
down into two parts: a queue script for a
particular queuing system and a user script for running the application code.
– Generating batch scripts from user requests is a common task implemented by a several portals (including Gateway and HotPage).
• A good first test service of interoperability.
• IU and SDSC support different queuing systems, so collectively they benefit from a shared service. (IU: PBS <==>SDSC: LSF, LoadLeveler,
NQS)
• Job & Host monitoring
– Has been built in the polling method.
Application Web Services
(AWS)
•
Application: specifically some code developed by the
scientific community.
– Example: Finite element codes, grid generation codes and so on.
•
AWS are designed to make scientific applications (i.e.
earthquake modeling codes) into Grid Resources.
•
We need a meaningful metadata model for applications
– Describe application-specific requirements
– Describe bindings of applications to host environments and to Web services in a general way that is independent of the particular
portal.
AWS Schema Structure
•
Two sets of XML schema:
–
Application Descriptors:
• describe abstract state.
• describe application options. Used by the application developer to deploy his/her service into the portal.
–
Application Instance Descriptors:
• describe particular instance states (ready, running, archived). • describe particular user choices and archive them for later
browsing and resubmission.
•
Schema sets are arranged hierarchically
–
Applications contain hosts
–
Schema are designed to be pluggable
AWS XML Descriptors
• Application description schema
– A “basic information” element that contains information such as application name, version, option flags.
– An “internal communication” element that contains child elements for describing input, output, and error fields for the code.
– An “execution environment” element that contains a list of core services needed to execute the application.
– An optional, generic parameter to hold arbitrary information about the application.
• Host description schema
– Contains information about the resource such as DNS name and IP address
– All of the information needed to invoke the parent application on that resource such as location of the executable, location of the workspace or scratch directory, and so on.
• Queue description schema
Sample generated user view of application code, Simplex: this form is
Security Requirements for Web Services
• Need mutual authentication between clients and User Interface Server (UIS)
– Clients are browsers: understand SSL but not Kerberos.
v provide a browser interface that will create a Kerberos TGT on the UIS for the user.
• Need a secure SOAP messaging system to connect UIS, the repository, and
service providers.
• What are security problems for Web Services?
– How do I prove identity?
– How do I verify the source of the message?
– How do I check message integrity? – How do I keep sensitive messages
private?
– How do I define and enforce access
Integration of Security into Web Services
• Authentication through single sign-on.
– Kerberos, PKI
– Distributed ticket system
– Getting assertions about authentication, authorization, user attribute
• SOAP security should be provided through standard interfaces to specific mechanisms.
• General methods are
– Message signing. – Message integrity. – Message encryption.
• Kerberos, PKI are specific mechanisms.
• Assertion is an XML document describing the information about authentication acts performed by subjects, attributes of subjects and authorization decisions, created with a
Proposal of Work: Web Services Security
•
Propose to investigate Web Services security.
–
SAML
•
Will define abstract security mechanisms
(authentication, etc.) for web services with
specific security bindings (Kerberos, PKI).
–
Message signing.
–
Message encryption.
•
Will implement mechanism-independent
Message Signing with SAML and Kerberos
• SAML expresses security assertions in XML.
• Demonstration Steps
– Establish both servlet session and GSS context between the UI and AS. – UI signs SAML assertion and SOAP
Body message with GSS Context’s wrap method.
– Service extracts SAML assertion and SOAP Body message with GSS
Context’s unwrap method from AS and verifies it.
• Implementations
– SAML assertion converted to Java data objects with Castor.
– Apache Axis modified to handle
Client login process for the user authentication
Initialize the secure context to get the
shared key.
Generate the assertion such as SAML,
WS-security.
Sign the assertion.
Add it to SOAP Header.
Sign the SOAP Body message.
The authentication service
Process the SOAP message
Check the assertion type such as SAML, WS-security and the security mechanism such as Kerberos, PKI.
Unwrap the assertion.
Test the user validity.
Unwrap the SOAP Body message.
Rebuild the SOAP message. Interne
Client An assertion-based authentication
Web service negotiation
• Needed for managing multiple versions of services
– Negotiation of quality of service
– For example, File Transfer service that has different bindings
• Motivating examples
– Secure Socket Layer (SSL) handshake protocol
• Authenticate uni- or bi-directionally using PKI certificate, and securely distribute shared secrets for exchanging the data.
• Negotiate the cipher suite, etc.
– Session Initiation Protocol (SIP)
• A standard of Internet Engineering Task Force, especially for Voice over IP. • An application-layer control protocol that can establish, modify and terminate
multimedia sessions or calls.
• Negotiate the compression algorithms, encryption algorithms, code book size, etc.
• Offer/Answer approach
– The offerer has the offer, for example, a set of protocols and services, service version which she wishes to use .
Proposal of Work: Web Service
Negotiation
• Will extend WSDL to support the metadata
about the negotiation.
• Will design and implement the negotiation
XML schema as the namespace in WSDL.
• Will design and implement the family of
Integrating the negotiation into Web Service
• Implement Web service negotiation through extensions to WSDL.
– Negotiation type may be specified in separate portTypes in the same WSDL document.
• The negotiation “portType” XML schema contains two elements:
– The “operation” element is intended to be extended by another URI that defines a standard negotiation message format.
– The “parameters” element is extended to contain the actual data used in the negotiation.
• Describe family of parameter XML schema which is applicable to the “parameter” element in the negotiation XML descriptor.
– Version picking (namespace: http://.../Negotiate/../Version) schema which contains a Version service name and a set of Version values.
– Protocol picking (namespace: http://.../Negotiate/../Protocol).
• The basic interaction of a Web service negotiation for version control
– The client-side process is as follows:
• For managing the operation messages between participants, we should pick a parameter family defined by a URI such as http://.../Negotiate/Version.
• sends itsparameters configuration and the URI of that configuration.
– The targeted SOAP server-side process is as follows:
• makes a decision when receiving the client’s parameter list and URI for the negotiation information.
Negotiation namespace
Application: GEM Portal Overview
•
Put basic Web services and architecture to work in GEM
computational web portal.
•
URL for portal :
h
ttp://complexity.ucs.indiana.edu:8282/jetspeed/index.jsp
•
Po
rtal testbed
– UI server: complexity.ucs.indiana.edu
– Backend services: danube.ucs.indiana.edu, grids.ucs.indiana.edu, solar.uits.indiana.edu, noahsark.ucs.indiana.edu
•
Requirements for enabling code interoperability: data
models and services
GEM Portal Architecture
Client Stubs
DB Service 1
JDBC
Job Sub/Mon And
File Service s
Operating
Portlet Based User
Interface
DB Service 2
JDBC HTT
P
SOAP SOAP
GEM Computing Portal
•
A number of simulation methods for studying earthquakes are
being developed by GEM consortium including:
–
Simplex, Disloc, GeoFEST (
JPL
)
–
Virtual California (
UC-Davis
)
–
PARK codes (
Brown
)
•
As codes become more widely used, problems emerge:
–
Need to manage information about distributed data sources:
multiple databases, sensors, simulated data.
–
Need to organize, manage information about multiple code
installation sites.
–
Need to simplify access to data, use of codes, and use of
visualization/analysis tools for broad range of users
Code Linkages in Initial System
Elastic Dislocation
Pattern Recognizers Viscoelastic Layered BEM
Data Service
• What are problems?
– Codes all use “legacy” text formats for describing input and output.
– Input and output data often combined with code-specific information, for example, number of iterations, starting temperature and so on.
– Data not always represented uniformly
• We designed and built the following:
– Data models: Fault, Displacement, Disloc and Simplex data XML schema – Programming interfaces to data
– Interfaces themselves need structural organization – Implementations of the interfaces
– Integration of the interfaces and implementations into our service architecture.
• The structural organization should allow extension to specific applications
– Anticipating integration of VC, PARK, GeoFEST, etc.
Browser Interface
User Interface Server
User selects codes,
resources, and code data.
HTTP
Disloc Data Service
Disloc Execution
Service SOAP/HTT
P User requests
translated to XML data formats using the remote service.
User Interface Server
Simplex Data
Service Disloc DataService
(1) Requests formatted Disloc output
data be pushed to Data Hub.
(2) XML (4) Requests and
(3) Signals Simplex to request
displacement
data from Data Hub.
Execution Host
Execution Host
Simplex and Disloc code share
Data Transfer Performance with SOAP
•
We classified four mechanisms for sending messages:
– SOAP : For this, We implemented “MessageTest” service which just take the message.
– SOAP with Attachments: We used “uploadFile” method in “FileService” Web service.
– WebFlow : “RemoteFile” service module.
– Plain Socket
•
Testing environments
– Server part: SunOS 5.8 (grids.ucs.indiana.edu)
– Client part
• Desktop PC (winnipeg.ucs.indiana.edu) • SunOS 5.8 (apollo.ecs.syr.edu)
– Message type : text file only
•
We tested two cases according to the domain name.
Conclusions - 1
• We defined a new service based architecture for computing portals for gaining interoperability and reusability.
• We defined interfaces for services and built several general purpose services.
– Job submission
– Job & Host monitoring – Context management – Script Generation
– File transfer and manipulation – Application service
• We designed and implemented a message-based security system for Web service security.
• We designed and implemented a negotiation system for Web Services. • We put our services to work in GEM computing portal.
• We designed and implemented a data sharing architecture (Using a new service based architecture can be extended for new services).
– Designed XML data models – Designed hierarchy of services – Designed translators
Conclusions - 2
• By designing and implementing several core portal services and
Application Web Services around Web services, we gain interoperability and reusability.
• The emphasis on the development of reusable services that can form the basis for multiple PSEs.
• The portal developer can construct specific implementations and
composites of primitive service components and can also provide services that may be shared among different portals.
• Application-specific services and data models that can be used to
encapsulate entire applications independently of the portal implementation. • User interfaces to application services become distributed portlets.
• Web service security is one aspect of our overall program for building Grid Computing Environments.
Future Work
•
Use of service architecture with proxy-style portal
front-ended by the aggregation portal
– Applications, Portal shell commands, Content services
– WSRP (Web Services for Remote Portlets) for “Pluggable” integration with all portals
•
Particular services needed
– The workflow management service for handling the web services using WSFL, or our own XML dialects which is needed for the computing portal.
