Architecture | Modular Enterprise Applications | Mark Nuttall
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This document discusses modularity and OSGi, including: - What modularity is and why Java needs it to reduce entanglement over time - An overview of Enterprise OSGi and how it brings enterprise technologies to OSGi - New features in OSGi Service Platform Release 4 such as a standard application model and bundle repository - A demonstration of a colors application that uses OSGi bundles and services
Architecture | Modular Enterprise Applications | Mark Nuttall
- 1. Modular Enterprise Applications Mark Nuttall, mnuttall@uk.ibm.com IBM WebSphere OSGi Applications development lead
- 2. Overview • Modularity and OSGi: what they are and why Java needs them • Enterprise OSGi • What’s new in the OSGi Service Platform Release 4 Early Draft 2011.09, and why it’s important • Demonstration
- 3. Modularity So what is Modularity? “(Desirable) property of a system, such that individual components can be examined, modified and maintained PCIe x16 independently of the remainder of the system. Objective is that changes in one part of a system should not lead to unexpected behavior in other parts.” VGA DVI www.cs.bath.ac.uk/~jap/MATH0015/glossary.html
- 4. Complexity and System Rot Traditional system Modular system Modular system Traditional system Time Time In a software system, entanglement is the primary cause of decay.
- 5. Java needs help: enforcing modularity makes entanglement less likely • Java unit of modularity = JAR • Enterprise apps are collections of JARs • But a JAR lacks the primary characteristics of modularity: People do this to software all the time! • It does NOT hide its internals • It does NOT declare its externals • The global Java classpath does NOT support versioning
- 6. What is OSGi? • “The dynamic module system for Java” – Mature 10-year old technology – Governed by OSGi Alliance: http://www.osgi.org – Used inside just about all Java-based middleware • IBM WebSphere, Oracle WebLogic, Red Hat JBoss, Sun GlassFish, Paremus Service Fabric, Eclipse Platform, Apache Geronimo, … Jar Jar Package Explicit exports Package Class Class Class Class Class Class Package Package Class Class Class Class Class Class Explicit dependencies 6
- 7. How does OSGi help reduce cost? • Enforces architecture and simplifies maintenance • Enables modular deployment • Enables co-existence of multiple versions of libraries – Simplifies independent evolution of applications – Better separation of concern between application and middleware • Enables truly dynamic update of modules within applications Bundle Bundle Package Explicit exports Package Class Class Class Class Class Class Package Package Class Class Class Class Class Class Explicit dependencies 7
- 8. OSGi Modules (aka Bundles) Classloader Bundle • A Jar plus OSGi Manifest, includes: Manifes t-Ver sion : 1.0 Bundle- Manif estV ersi – Bundle Identity Classloader Bundle – Exported Packages Manifes t-Ver sion : 1.0 Bundle- Manif estV ersi Classloader Bundle – Imported Packages Manifes t-Ver sion : 1.0 Bundle- Manif estV ersi • Dependency resolution Classloader “wires” bundles into Bundle a dependency graph Manifest-Version: 1.0 • Each gets its own Bundle-ManifestVersion: 2 class loader • Classloading delegates via graph Manifest-Version: 1.0 Bundle-ManifestVersion: 2 Bundle-Name: My Example Bundle Bundle-SymbolicName: com.my.bundle Bundle-Version: 1.0.0 Export-Package: com.something.i.provide;version="1.0.0" Import-Package: com.something.i.need;version="[1.1,2.0)"
- 9. Dynamic Lifecycle Bundle • Bundles have a dynamic lifecycle • Can come and go independently • APIs enable graceful reaction to changes
- 10. OSGi Services service Consumer get register Provider Bundle Bundle listen • Publish/find/bind service model – Fully dynamic – Local – Non-durable • Primary mechanism for bundle collaboration • POJO advertised with properties and/or interface and/or class
- 11. OSGi Enterprise Specification • Enterprise 4.2: Released 22 March 2010 – OSGi Enterprise Expert Group (EEG) • Brings Enterprise technologies and OSGi together • Using existing Java SE/EE specifications: – JTA, JPA, JNDI, JMX, WebApps… • Adds Spring-derived Blueprint component model and DI container • New in the OSGi Service Platform release 4 early draft 2011.09: – Standard application model – Bundle repository • Java EE provides the core enterprise application programming model • OSGi encourages modular design, simplifies reuse, and enables dynamic module updates
- 12. OSGi Bundle Repository • Standardizes the entities required to resolve requirements – Used by the Subsystems specification for deployment • Environment – enables context and policy • Resolver – similar to runtime framework resolver • Repository – provides candidate solutions to requirements • Repository XML – interchange XML Repository1 Resolver Environment Repository2 XML Subsystem Repository3
- 13. Subsystems: Disclaimer • Subsystems is an in-progress RFC. What follows is a snapshot in time of the expert group thinking and is subject to change.
- 14. Subsystems: Motivation • Enterprise Java platforms are awash with bundle collections – Apache Aries – Applications – Apache Geronimo - Applications – Apache Karaf – Features – Eclipse Virgo – Plans, PARs – IBM WebSphere Application Server – Applications, Composites, Liberty Features – Oracle GlassFish – Applications – Paremus Service Fabric – Systems • Crying out for standardization – Portability – Tools – Ecosystem
- 15. Subsystems Model: Hierarchy • Most common model is subsystem hierarchy and so Subsystems are no subsystem different – Each has 1 parent subsystem – Each can have many children subsystem subsystem – Children of the same parent are siblings • Visually represented by subsystem subsystem containment
- 16. Feature Subsystems • Collection of Resources (e.g. feature Bundles) bundle • Shared life-cycle • Can be nested feature • No isolation or affinity bundle • Repository-based bundle provisioning bundle • Examples: Karaf Features, Virgo unscoped Plans bundle bundle
- 17. Composite Subsystems • Coarse-grained sub-assembly bundle module • Isolated composite • Explicit share in/out bundle • Affinity • Repository-based bundle provisioning bundle • Examples: RFC 138 Composite Bundles*, WebSphere Composite Bundles bundle bundle *old design prior to resolver hooks
- 18. Application Subsystems • Model for hosted applications application bundle • Isolated • No sharing out, implicit bundle sharing in bundle • Affinity • Repository-based provisioning bundle bundle • Examples: Aries Application, Virgo Scoped Plans, Virgo PARs
- 19. Example Combination • Subsystem Types can be framework mixed and matched application application • Example shows: – Features used to assemble a Composite composite – Composite providing a feature feature ‘platform’ to Applications feature
- 20. Portability • Subsystem Manifests are portable to a point Subsystem Definition – Target Environment + Transitive Dependencies must support the required resource implementation Transitive types (e.g. Blueprint, WAB, DS, Dependencies etc) • Transitive dependencies Target Environment may be portable – Different Target Environments likely to require different Transitive Dependencies
- 21. Packaging • Packaged in a Subsystem my.first.subsystem.ssa Archive OSGI-INF/SUBSYSTEM.MF • A zip file with .ssa extension: OSGI-INF/DEPLOYMENT.MF – Subsystem Manifest (optional) – Deployment Manifest (optional) an.osgi.bundle-1.0.0.jar – Resources (optional) an.osgi.bundle2-1.0.0.jar
- 22. Start with an empty Example Composite Composite ACTIVE
- 23. Application Subsystem Example installed and resolved Composite ACTIVE Application RESOLVED bundle RESOLVED transitive bundle RESOLVED
- 24. Second Application Subsystem installed and Example started Composite ACTIVE Application RESOLVED Application ACTIVE bundle bundle RESOLVED ACTIVE transitive bundle transitive bundle ACTIVE ACTIVE
- 25. Second Application Example Subsystem uninstalled Composite ACTIVE Application RESOLVED Application UNINSTALLED bundle bundle RESOLVED UNINSTALLED transitive bundle transitive bundle RESOLVED UNINSTALLED
- 26. First Application Subsystem Example uninstalled Composite ACTIVE Application UNINSTALLED Application UNINSTALLED bundle bundle UNINSTALLED UNINSTALLED transitive bundle transitive bundle UNINSTALLED UNINSTALLED
- 27. Subsystems: Summary • With the publication of the next OSGi Service Platform specification, subsystems will be the standard way to manage groups of resources • Version ranges allow flexibility in resource selection • Subsystem types define sharing semantics • Deployment definition – locks down versions and sharing – Identifies transitive dependencies • API enables management of Subsystem life-cycle
- 28. Demo Time: Colors by WebSphere
- 29. Colors by WebSphere: Bundles and Services colors.provider.red colors.web colors.blender colors.provider.green colors.provider.blue colors.api
- 30. Colors by WebSphere: Color services Color services colors.provider.red colors.web colors.blender colors.provider.green colors.provider.blue colors.api
- 31. Colors by WebSphere: Color services Adjustment Service colors.provider.red (Extension Point) colors.web colors.blender colors.provider.green colors.provider.blue colors.api
- 32. Summary • Modularity and OSGi: what they are and why Java needs them • Enterprise OSGi • What’s new in the OSGi Service Platform Release 4 Early Draft 2011.09, and why it’s important • Demonstration
- 33. Thank you! Any questions?