Monoliths are so 2001 – What you need is Modularity
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The document discusses the shift from monolithic architectures to modular systems in software development, emphasizing the need for capturing architectural knowledge and enforcing modularity through OSGi. It covers the challenges faced in traditional Java EE modularity and introduces OSGi bundles as a solution for better dependency management, resource handling, and dynamic lifecycles. A case study on the 'Acme Air' application illustrates the gradual process of dismantling monolithic structures and adopting modular practices.
Monoliths are so 2001 – What you need is Modularity
- 1. © 2015 IBM Corporation Monoliths are so 2001 – What you need is Modularity Graham Charters, STSM, WebSphere Liberty Repository & OSGi Applications Architect Ian Robinson, Distinguished Engineer, WebSphere Foundation Chief Architect
- 2. Agenda • Monoliths & Modularity • Modularity and Java • Introduction to OSGi • Dismantling the Monolith • A Case Study – Acme Air • What’s new in OSGi Applications • Summary 1
- 4. Why Monoliths • No project sets out to create a monolith • Projects evolve • Teams evolve • Architecture knowledge is lost leading to sub-optimal decisions
- 5. How do we preserve knowledge? • Design documentation? • Wiki? • Email? • Work items? • IRC? • Brain? • Developers make the decisions, and where do they hang out? 4 We need to capture and enforce the architectural knowledge in the code
- 6. Modularity • Concept of Modularity in Software dates back to the 1960 • For a module systems to preserve architectural knowledge it needs the follow qualities • Reflect the right level(s) of architectural granularity • Support the Reuse/Release Equivalence Principle • Capture modularity information in the code • Enforce modularity 5 None of your business What I can provide to you What I will need from you
- 8. 7 Base Java modularity is inadequate • Classes too fine-grained • Jars are packaging with no explicit requirements/capabilities • Linear classpath Java EE modularity is inadequate • Across apps - each archive typically contains all required libraries • Common libraries/frameworks get installed with each application • Multiple copies of libraries in memory • Within apps - 3rd party libraries consume other 3rd party libraries leading to conflicting versions on the application classpath. webB.war WEB-INF/classes/servletB.class WEB-INF/lib/json4j.jar WEB-INF/lib/commons-logging.jar WEB-INF/lib/junit.jar… webC.war WEB-INF/classes/servletC.class WEB-INF/lib/json4j.jar WEB-INF/lib/commons-logging.jar WEB-INF/lib/junit.jar… plankton.v1 plankton.v2 Modularity Issues in Java EE
- 10. 9 Bundle Manifest-Version: 1.0 Bundle-ManifestVersion: 2 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)" Bundle Bundle Bundle Manifest-Version : 1.0 Bundle-ManifestVersi Manifest-Version : 1.0 Bundle-ManifestVersi Manifest-Version : 1.0 Bundle-ManifestVersi OSGi Modules (aka Bundles) • A Jar plus OSGi Manifest, includes: • Bundle Identity • Exported Packages • Imported Packages • Dependency resolution “wires” bundles into a dependency graph • Each gets its own class loader • Classloading delegates via graph Classloader Classloader Classloader Classloader
- 11. 10 Dynamic Bundle Lifecycle • Bundles have a dynamic lifecycle • Can come and go independently • APIs enable graceful reaction to changes Bundle INSTALLED RESOLVED UNINSTALLED STARTING ACTIVE STOPPING install update refresh uninstall update refresh stop policy resolve uninstall
- 12. 11 Local Services • Publish/find/bind service model • Fully dynamic • Local • Non-durable • Primary mechanism for bundle collaboration • POJO advertized with properties and/or interface and/or class service Provider Bundle Consumer Bundle registerget listen
- 14. Background • First surfaced to applications in a WAS v7 Feature Pack • http://www-01.ibm.com/software/webservers/appserv/was/featurepacks/ • Modular development, deployment and management • Blueprint (Standardized Spring Component Model) • Web applications (Java EE 5) • Remote Services and Heterogeneous Assembly (SCA) • Included in the WAS Base in v8 and continually extended: • Java EE 6 Web technologies • Post-deployment configuration • Performance metrics • In-place Update • Application Extension • Modular EJB • Blueprint Role-based Security • OSGi Applications Web Console • Liberty Profile support 13
- 15. Component Models Category Full Profile Liberty Profile Presentation Servlet, JSP, JSF Servlet, JSP, JSF Business Blueprint*, EJB Blueprint* Persistence JPA, JDBC JPA, JDBC Integration JAX-RS, JMS, SCA JAX-RS, JAX-WS, JMS 14 Component models for enterprise Web applications Re-use rather than re-invent • Java EE, Spring *some differences in supported namespaces
- 16. Web Application Bundle • Web Application Bundle (WAB) = WAR + OSGi metadata • Web-ContextPath: header used to specify default context root • OSGi Manages • Module Lifecycle • Classloading (opportunity to split out WEB-INF/lib) • Service Integration • Web Container Manages • Web component life-cycle, serving, etc... webC.war logging f/w persistence f/w MVC f/w webB.war logging f/w persistence f/w MVC f/w webA.war logging f/w persistence f/w ... WEB-INF/classes/servletA.class WEB-INF/web.xml WEB-INF/lib/… webA.jar WEB-INF/classes/servletA.class WEB-INF/web.xml META-INF/MANIFEST.MF webA.jar WEB-INF/classes/servletA.class WEB-INF/web.xml META-INF/MANIFEST.MF webA.jar WEB-INF/classes/servletA.class WEB-INF/web.xml META-INF/MANIFEST.MF logging f/w persistence f/w ... These can become shared bundles
- 17. Bundle Blueprint Components and Service • Dependency Injection container • Standardizing established Spring conventions • Configuration and dependencies declared in Blueprint XML • Standardization of Spring “application context” XML • Extended for OSGi: publish/consume components as OSGi services • Simplifies unit test outside either Java EE or OSGi r/t • Integrated into server runtime to simplify deployment & support 16 dependencies injected publishes service consumes service Blueprint container scoped by a bundle (one per bundle). Multiple <blueprints /> per container. A static assembly and configuration of beans (POJOs) Blueprint managed bundle
- 18. Brightness Blueprint Extensions • Namespaces extend core component model • Transactions • Resource References (Full Profile) • JPA integration • Security (Full Profile) • Third-party (Liberty 8.5.5.3) <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:sec="http://www.ibm.com/appserver/schemas/8.0/blueprint/security" xmlns:tx="http://aries.apache.org/xmlns/transactions/v1.0.0"> <service id="adjustmentService" ref="BrightnessDeltaBean" interface="colors.adjustment.api.BrightnessService"> </service> <bean id="BrightnessDeltaBean" class="colors.brightness.BrightnessDelta"> <sec:access-constraint method="setBrightnessDelta" role="adjuster" /> <tx:transaction method="*" value="Required" /> <jpa:context property="em" unitname="brightnessUnit"/> <property name="delta" value="100"/> </bean> </blueprint>
- 19. EJB Bundle • EJB Bundle = EJB Jar + OSGi Metadata • Export-EJB: Opt-in header for EJB Bundles – Existence: process bundle for EJBs – Absence: do not process bundle for EJBs, even if it contains them • Header value governs registration of EJBs as OSGi Services – Excludes Message-Driven and Stateful beans – Best practice: only export EJBs to be shared outside bundle • EJBs run in the same WAS EJB Container • Uses OSGi for Classloading and Life-cycle 18 Example Meaning Export-EJB: Process all EJBs and register them as OSGi services Export-EJB: BlogBiz, BlogPersistence Process all EJBs, register BlogBiz and BlogPersistence as services if they exist Export-EJB: NONE Process all EJBs but don’t register them as OSGi services
- 20. Persistence Bundle • Persistence Bundle = Persistence Archive + OSGi Metadata • Meta-Persistence: opt-in header • Identifies the location of the persistence xml file • Defaults to META-INF/persistence.xml • Datasource lookup mechanisms: <jta-data-source> <!-- component name is the name of a blueprint resource reference --> blueprint:comp/blueprint_component_name </jta-data-source> <jta-data-source> osgi:service/javax.sql.DataSource/(osgi.jndi.serviceName= jndi_name_of_the_data_source) </jta-data-source> <jta-data-source> jndi_name_of_the_data_source </jta-data-source>
- 21. .eba OSGi Application • Isolated, cohesive collection of bundles • Defined by application manifest • Configuration by exception • Deployed as .eba archive (zip file) • Provisioning resolves application against archive contents and configured bundle repositories APPLICATION.MF Application-Name: Color Blender Application Application-SymbolicName: colors.blender.simple.app Application-ManifestVersion: 1.0 Application-Version: 1.0.1 Manifest-Version: 1.0 Application-Content: colors.blender;version="[1.0.0,2.0.0)", colors.provider.green;version="[1.0.0,2.0.0)", colors.provider.red;version="[1.0.0,2.0.0)", colors.web;version="[1.0.0,2.0.0)", colors.provider.ejb.blue;version="[1.0.0,2.0.0)" Application-ImportService: colors.adjustment.api.BrightnessService Application-Name: Color Blender Application Application-SymbolicName: colors.blender.simple.app Application-ManifestVersion: 1.0 Application-Version: 1.0.1 Manifest-Version: 1.0 Application-Content: colors.blender;version="[1.0.0,2.0.0)", colors.provider.green;version="[1.0.0,2.0.0)", colors.provider.red;version="[1.0.0,2.0.0)", colors.web;version="[1.0.0,2.0.0)", colors.provider.ejb.blue;version="[1.0.0,2.0.0)" Application-ImportService: colors.adjustment.api.BrightnessService colors.web colors.blender
- 22. OSGi Application Provisioning • Application manifest allows version ranges for contents • Deployment Manifest (optional) locks down exact versions • Provisioning resolves application against archive contents and configured bundle repositories • Non-content bundles satisfy unresolved application package and service dependencies • shared between applications on same server .eba APPLICATION.MF DEPLOYMENT.MF colors.api colors. web colors. blendercolors. provider. blue Shared Bundles colors. blender OSGi Application colors. provider. blue colors.api colors. web
- 24. Adoption Strategies • Favoured Java EE Approach: 1. Replicate existing classloading in OSGi using bundle fragments 2. Incrementally separate out individual bundles 3. Adopt OSGi best practices • Considers Java EE classloading and component models • Surfaces OSGi early, and incrementally - a staged approach 23 beans core ejb3 entities json-proxy soap wsappclient streamer web app-host logcoreejb3 wab web app-host logcoreejb3 wab web log http://www.slideshare.net/GrahamCharters/modularizing-existingenterpriseapplicationsos-gicommunityevent2012v01
- 25. Stage 1: Understanding the starting point • Java EE prescribes a hierarchical classloading model • Assuming “parent first” and “multiple”: • Each Application has own classloader • Each WAR has own class loader • WAR has visibility to Application classes • WAR prefers Application classs, Application prefers System classes, etc... • OSGi modularity enforced through class visibility using classloaders • Migration strategies need to consider the impact of this change • e.g. replicate visibility relationships of existing application in OSGi 24 Bootstrap Extensions System Application Application WAR WAR WAR
- 26. Stage 1: Replicating Java EE classloading • Preserve Application and WAR roles • Application -> Application Host Bundle • Add application modules to fragments of host bundle • Web App Archive -> Web Application Bundle • Add WEB-INF/classes to Bundle-Classpath • Extract WEB-INF/lib jars and add as fragments of Web Application Bundle • We now have two classloaders just as we did in Java EE • We also have full visibility of the modules 25 System Application WAR app-host logcoreejb3 wab web
- 27. Stage 2: Factoring out Bundles • Now the application’s running in OSGi we can start to split out the fragments as independent, re-usable bundles • Strategy: • Do one fragment at a time • Start with the leaf dependencies – Wab bundle contents first, then the app bundle – Project build dependencies help with identification – Third-party libraries – “shared libraries” (if runtime supports this concept) • Detach from host and calculate the package imports & exports 26 wab web wab web Fragment-Host: wab Export-Package: daytrader.web Import-Package: daytrader.web
- 28. Stage 3: Incrementally Adopt Best Practices • Stage 2 documents the ‘as-is’ architecture, warts-‘n’-all • OSGi Best Practices show how to make the most of OSGi http://www.ibm.com/developerworks/websphere/techjournal/1007_charters/1007_charters.html • Adopting best practices leads to: • High cohesion - bundles with clear and distinct roles in the architecture • Loose coupling - flexible, but necessary, dependencies • ...which all leads to greater agility, flexibility and re-use • Development teams can understand and explain the architecture and are no longer afraid to change the code • Applications can evolve and new application can be created at a pace that enables, rather than inhibits, the business 27
- 30. Acme Air • A Sample Java EE Web Application • Key Technologies • Web content - html, JavaScript • REST APIs - JAX-RS • Persistence – JPA • Spring • Built using Maven • Deployed as a WAR with all the dependencies inside (WEB-INF/lib) acmeair-webapp.war acmeair-common.jar acmeair-service.jar springxxx.jar WEB-INF/classes/xxx.class WEB-INF/web.xml WEB-INF/lib/… ... 29
- 31. Stage 1: 30
- 32. Stage 1 - 1 = 0: Single Bundle • Single monolithic bundle • Build a WAB not a WAR • Web–ContextRoot • Bundle-Classpath • Package imports • Uses JPA so also make it a Persistence Bundle • Change use java:comp/env to osgi:service • Address classpath issues (e.g. Spring @ComponentScan, file loading) 31 acmeair-webapp.war acmeair-common.jar acmeair-service.jar springxxx.jar WEB-INF/classes/xxx.class WEB-INF/web.xml WEB-INF/lib/… acmeair-webapp-bundle.jar WEB-INF/classes/xxx.class WEB-INF/web.xml META-INF/MANIFEST.MF ... <plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> <version>2.5.3</version> <extensions>true</extensions> <configuration> <instructions> <Web-ContextPath>/acme.air.osgi</Web-ContextPath> <Embed-Dependency>*;scope=compile</Embed-Dependency> <Bundle-Classpath>WEB-INF/classes</Bundle-Classpath> <Embed-Transitive>true</Embed-Transitive> <Meta-Persistence> WEB-INF/classes/META-INF/persistence.xml </Meta-Persistence> <Import-Package> !javax.resource, !javax.resource.cci, !javax.resource.spi, ... javax.*, org.xml.sax, org.w3c.dom </Import-Package> <_wab>src/main/webapp</_wab> </instructions> </configuration> </plugin> acmeair-common.jar acmeair-service.jar springxxx.jar ...
- 33. Stage 1: OSGi Application • Build an OSGi Application (EBA) to deploy the WAB • Eba-maven-plugin generates application manifest based on pom configuration 32 acmeair-webapp-bundle.jar acmeair.eba META-INF/APPLICATION.MF <plugin> <groupId>org.apache.aries</groupId> <artifactId>eba-maven-plugin</artifactId> <version>1.0.0</version> <extensions>true</extensions> <configuration> <generateManifest>true</generateManifest> <instructions> <Application-SymbolicName> ${project.artifactId} </Application-SymbolicName> </instructions> </configuration> </plugin> Application-ManifestVersion: 1 Application-SymbolicName: acmeair-eba Application-Version: 1.0.0.SNAPSHOT Application-Name: acmeair osgi application Application-Description: AcmeAir Application Application-Content: net.wasdev.wlp.sample.acmeair-webapp-bundle;version="1.0.0.SNAPSHOT"
- 34. Stage 1: Fragments • Fragments used to separate out “modules” from WAB without affecting classloading • Update EBA to include Fragments • First opportunity to see the true package dependencies • Opportunity for small refactoring (e.g. persistence.xml from WAB to persistence fragment) 33 acmeair-webapp-bundle.jar WEB-INF/classes/xxx.class WEB-INF/web.xml META-INF/MANIFEST.MF springxxx.jar acmeair-common-bundle.jar acmeair-service-bundle.jar acmeair-service-jpa-bundle.jar <plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> <version>2.5.3</version> <extensions>true</extensions> <configuration> <instructions> <Fragment-Host> net.wasdev.wlp.sample.acmeair-webapp-bundle </Fragment-Host> </instructions> </configuration> </plugin> persistence.xml
- 35. Stage 2: Bundles • Detach Fragments from Host • Move opt-in headers from Host to new bundles • Export packages from Host, if necessary (e.g. Spring) • Separation Issue: webapp bootstraps spring beans from service-jpa then looks them up 34 acmeair-webapp-bundle.jar WEB-INF/classes/xxx.class WEB-INF/web.xml META-INF/MANIFEST.MF springxxx.jar acmeair-service-bundle.jar acmeair-service-jpa-bundle.jar acmeair-common-bundle.jar persistence.xml <plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> <version>2.5.3</version> <extensions>true</extensions> <configuration> <instructions> <Meta-Persistence> META-INF/persistence.xml </Meta-Persistence> </instructions> </configuration> </plugin>
- 36. Stage 2: Bundles...not quite • Webapp uses a singleton “ServiceLocator” to get the Spring beans • Webapp ServiceLocator bootstraps the Spring application context by trying to load config from the service-jpa bundle but can’t find it • @ImportResource({"classpath:/spring-config.xml"}) • These modules are too tightly couple and so can’t function independently. 35 acmeair-webapp-bundle.jar WEB-INF/classes/xxx.class WEB-INF/web.xml META-INF/MANIFEST.MF springxxx.jar acmeair-service-jpa-bundle.jar @ImportResource({"classpath:/spring-config.xml"}) spring-config.xml
- 37. Stage 2 & 3: Bundles...almost • ServiceLocator is acting as a Service Registry. OSGi has one of those. • Bundle Activator used to bootstrap Spring application context and register bean services • Also needed to register EntityManager service for Spring • Webapp changed to load services from Service Registry 36 acmeair-webapp-bundle.jar WEB-INF/classes/xxx.class WEB-INF/web.xml META-INF/MANIFEST.MF springxxx.jar acmeair-service-jpa-bundle.jar spring-config.xml SpringActivator @ImportResource({"classpath:/spring-config.xml"}) ic.lookup("osgi:service/acmeair.CustomerService")
- 38. Stage 2 & 3: Bundles • But... there’s still a slight issues... lifecycle • Can’t bootstrap Spring if the Persistence support is not ready • Could “sleep”, but for how long? • Solution: use a service lifecycle- aware component model (Blueprint) 37 acmeair-webapp-bundle.jar acmeair-service-jpa-bundle.jar spring-config.xml acmeair-common-bundle.jar EntityManagerFactory <blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"> <bean id="SpringContextInitializerBean" class="com.acmeair.jpa.service.config.SpringContextInitializer"> <property name="ctxt" ref="blueprintBundleContext" /> <property name="emf" ref="emf" /> </bean> <reference id="emf" interface="javax.persistence.EntityManagerFactory“ /> </blueprint> blueprint.xml
- 39. Was it worth it? • A set of modules re-usable at different levels • Persistence • Local Domain Services • Remote REST Services • Looser-coupling and higher cohesion • No persistence content in the Web front-end • Spring isolated to the module that uses it • Flexible lifecycle 38 acmeair-webapp-bundle.jar acmeair-service-jpa-bundle.jar acmeair-common-bundle.jar
- 40. What’s New
- 41. What’s new in WebSphere OSGi Applications Liberty had addressed a number of top customer requirements through 2014 • Customer Blueprint Namespace Handlers • Use cases: CXF, Camel, Config Adnim, etc… • External Bundle Repositories • Use cases: Rational Asset Manager, Nexus integration • Local Application to application integration • Use cases: Application interaction, ‘extension’ • JAX-RS & JAX-WS • Use cases: Integration & Interop • Subsystems (beta) • Uses cases: extension and in-place update • Be sure to raise RFE to help us prioritize your needs • https://www.ibm.com/developerworks/rfe/
- 42. Summary
- 43. Summary • Enforce right-scale modularity is key to preserving architectural knowledge • Even relatively simple applications can become entangled in the absence of a good modularity • A methodical approach to adopting OSGi can deliver results early and dismantle the monolith • WebSphere Application Server Liberty Profile is now an even better platform for Enterprise OSGi
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