SCA Details for Your SOA Environment

At WebSphere Technical Exchange 2006, Eric Erpenbach--Advisiory Software Engineer working on WebSphere Process Server Development--spoke about how SCA is implemented in WPS.

Service Component Architecture Review

• Core component model for SOA applications
  • COnsistent way of describing components as services
  • Consistent client programming model
• SCA runtime environment in WebSphere Process Server and WebSphere ESB
  • Component wiring supports both synchronous and asynchronous invocation
• Impl in WPS and WESB is IBM's, not Apache Tuscany
  • Tuscany will be in the SOA Feature Pack

SCA Implementation in WPS

Component Options

• Components can be called and can call other components
  • Exports provide services
  • Imports indicate external service dependencies
• Deployment unit is a module
• Binding/wiring options
  • SCA
  • JMS
  • Web services
  • JCA
  • SLSB (import only)
• Component references
  • JSP
  • EJB
  • Java Class
• Component types
  • Process (BPEL)
  • Huamn Task
  • Business Rule Group
  • Business State Machine
  • Java
  • Mediation (ESB)
• Questions asked:
  • JMS format? Depends on your application
  • JCA adapters? We know IBM's work with SCA, other vendors' may not.
  • Limitations on parameter/return types of imports/exports? Defined by XSD, represented by an SDO. WPS supports anything SDO does.
  • Handles XSD choice? Probably in runtime, perhaps not in WID tooling.
  • Requirement to have everything in one EAR? Only if components are in one module.
  • How would you call a component from a Portlet? Through a binding of the export, such as the Web services binding.
  • Why not an SLSB export binding? Doesn't make sense for an SCA to act as an EJB home/bean.

SCA Quality of Service

• Qualifiers provide configurations options
  • Local or global transaction
  • When request and/or response should expire

Component Invocation Patterns

• Synchronous
• Pseudo Synchronous
  • Export has asynchronous API, invokes component synchronously (Service Activator)
• Asynchronous
• Callback
  • Import has a synchronous API, waits asynchronously for a response

SCA Message

• Contains data between service consumer and provider
• SOAP message
  • SCA message header
    • SCA system headers
      • Interaction header: Source, destination, and interaction type
      • Async header: Asynchronous interaction info
    • QoS headers
  • SCA message body
    • Business Objects/Busines Graph/SDO or Java objects
    • Exception details

SCA to Runtime Artifact Mapping

Type	Module	Export	Component	Import
J2EE	EAR	remote SLSB, opt MDB	local SLSB	EJB or service client, opt MDB

• queued messaging: similar, but with different JNDI bindings

SCA Invocation Styles

• Synchronous Intra-Module: SCA messages are passed by reference within the same module
• Synchronous Inter-Module (1 server): SCA messages are passed by value between modules, even within the same server
• Synchronous Inter-Module (2 servers): SCA messages are passed by value between modules/servers using RMI-IIOP
• SCA Asynchronous Intra-Module: SCA message is put in Component 1's import queue, forwarded to Component 2's request queue, received by Component 2's MDB
• SCA Asynchronous Inter-Module (1 server): SCA message is put in Import's import link queue for Module 1, forwarded to Module 2's export link queue, forwarded to Export's request queue, received by Export's MDB
• SCA Asynchronous Inter-Module (2 servers): Similar, communication between servers is between two SIBus messaging engines
• Questions:
  • Can we have two BPEL components in the same module? In 6.0.2, yes, but keep long running processes in their own module to make upgrading the process easier.
  • 6.0.1 merges an asynchronous connection to an import with an asynchronous connection to an export. They're effectively one asynchronous connection, not two.

SCA Failures

Events, ntoficaions, and exceptions

• Business exception
  • Sync
  • Async request/response
• System exception
  • Sync
  • Async
• Recovery service handles most errors

Recovery service for failed invocations

• WPS has built-in recovery services
  • Custom SIBus destinations for exceptions, MDBs for processing them
• If MDB cannot process message, moves it to exception destination, Failed Events DB
• Failed Event Manager: admin console provides inspection, modification, resubmission, deletion
• Q: Is this in Tuscany/SOA Feature Pack? No, added value of WPS.

Import/export Bindings

Web services binding for import/export

• Web service asynchronous request to an import is short-circuited to sync (as of 6.0.1.1)
• Web service receive, external consumer invokes WS binding on module export
  • Async between export and component is short-circuited

JMS binding for import/export

• Method binding available for operations
• Import puts JMS message on specifid destination
  • Async wiring to import is short-circuited

Future

• 6.0.2 has native WMQ support
• Additional bindings can easily be added
• SCA is fundemental for SOA

That was the end of the talk.