Karaf - When OSGi Modularity meets Java world

1. KARAF - WHEN OSGI
MODULARITY MEETS JAVA
WORLD
Justinas Šlekas

2. Modularization
• Ideas raised in the early 70s
• High Cohesion
• Low Coupling
• Manage growing complexity
• Modularization minimizes complexity by creating proper boundaries
between the parts that compose system
• Support dynamic extensibility
• Properly modularized systems are easier to maintain and extend
• Changes are more localized and affect less of the overall system

3. Object-Oriented
One of the primary goals of object oriented programming
(OOP) was, and still is,
RE-USE
It has mostly failed in that goal 

4. What went wrong?
Focus in OOP was on encapsulation of instance variables,
which is some form of modularization, but granularity is too
small
Coupling
• Classes can almost never be used in isolation, they depend on
other classes
• Those classes depend on other packages, which depend on other
JAR’s…
• OO systems become tangled webs quickly

5. Module?
Module should define:
• Identity and scope
• Unit of deployment
• Dependencies
• What it provides to other modules

6. What is module?
A module is a self-contained component of a
system, often interchangeable, which has a well-
defined interface to the other components.

7. Software Development Goal
One system that can evolve over time and modules can be
replaced without impacting the other modules.

8. Software Development Goal (2)
Multiple systems can be assembled in different products
and do not have to be implemented again and again.

9. Modularity
• Total control over library versions and dependencies,
different versions of the same library will happily coexist in
the same container
• Decouple system and application modules between each
other
• Share classes and dependencies
• Increase development agility, testing and version updating
• Isolate changes within your components
• Make your server go on a diet (Deploy exactly the
modules and frameworks you’ll need, and no more)

10. Introduction to OSGi
OSGi™ - The Dynamic Module System for Java
Formerly Open Services Gateway Initiative
Driven by OSGi Alliance - consortium of vendors
Non-profit corporation founded in 1999
Mission - Build ecosystem to support component
based development in Java

11. OSGi is about…
Module system for the Java platform
- Building systems from components
- Includes visibility, security rules, dependency management and
versioning control
Dynamic
- Installing, starting, stopping, updating modules, all dynamically at
runtime
- No downtime or 24/7 are the terms customers like to hear
Service-oriented collaborative model
- POJOs can be registered as services, consumed and managed
inside a VM, again, all dynamically at runtime

12. OSGi Architecture and Layers
The OSGi Platform specifies a modular
architecture for dynamic component based
systems
- Execution Environment
- Module Layer
- Life Cycle Layer
- Service Layer
- Security
Introduces Bundles as modules

13. OSGi Architecture and Layers
L0 - JRE Level
•OSGi Minimum Execution Environment
•CDC/Foundation
•JavaSE-6
•JavaSE-7
…
L1 - Creates the concept of modules
(bundles) that use classes from
each other in a controlled way
according to system and bundle
constraints. Deals with packaging,
versioning and dependencies

14. OSGi Architecture and Layers (2)
L2 - Manages the life cycle of a bundle
• Fine grained events for application and
component lifecycle, e.g.: installing,
starting, stopping, updating
• Standard API for registering, listening,
and acting on events
• No VM restarts
L3 – Provides a
publish/find/bind in-VM
service model
• Standard methods for
registering service instances
• Discover and bind to services
from other components

15. Interaction between the layers

16. Bundle
Bundle is a module in OSGi terminology
- Simply a JAR file plus module metadata stored in jar manifest
Bundle Identity
Dependencies
Versioning
What does a bundle JAR contain?
- Java classes (i.e., standard JAR file content)
- Resources (e.g., configuration files, images, etc.)
- Native code
- Embedded JAR files
Bundles can have their own classpath
A bundle JAR file can be both a standard JAR file and a
bundle at the same time

17. Anatomy of a Bundle

18. Bundle manifest
META-INF/manifest.mf
Bundle-ManifestVersion: 2
Bundle-SymbolicName: org.apache.servicemix.kernel.filemonitor
Bundle-Version: 2.0.0.0
Bundle-Name: Apache File Monitor
Bundle-Vendor: Apache Foundation
Bundle-RequiredExecutionEnvironment: J2SE-1.7
Bundle-Classpath: ., libmonitor.jar, libtest.jar, libreport.jar
Bundle-Activator: org.apache.servicemix.filemonitor.FileMonitorActivator
Bundle-Description: This bundle monitors directory for new deployments
Import-Package: org.apache.commons.logging,
org.apache.commons.io;version="1.4“,
javax.servlet;version=“[2.4,2.5]" ,
org.osgi.service.packageadmin
Export-Package: org.apache.jmx.facade,
org.apache.servicemix.kernel.filemonitor; version="1.0.0.0“

19. Bundles Dependencies
By default, none of the classes in a bundle are visible from
any other bundle
Export packages from the source bundle and then import
them into the target bundle
Import-Package: org.apache.commons.logging,
org.apache.commons.io;version="1.4“,
javax.servlet;version=“[2.4,2.5]" ,
org.osgi.service.packageadmin
Export-Package: org.apache.jmx.facade,
org.apache.servicemix.kernel.filemonitor; version="1.0.0.0“

20. Multi-version support

21. Controlling Dependencies

22. Bundle-to-Bundle dependency

23. Bundle Fragments

24. Bundle Life Cycle

25. Lazy Bundles
Bundles can be activated on demand
- Defer the creation of the bundle class loader and
activation of the bundle until the bundle is first used
- Can save resources and initialization time on startup
- Triggered by classloading event

26. Bundle Activator
- Bundle-Activator: Like main() for your bundle
- Bundles can hook into their life cycle by implementing
a bundle activator interface
- Notifies them when they are started/stopped
- Gives them access to their bundle context
• Which is how they access framework capabilities, e.g.:
 Bundle life cycle management
 Publishing or looking up services
- Simple Java interface

27. Bundles - Summary

28. OSGi classloading

29. A class space for a given bundle can
contain classes from
• The parent class loader (normally java.* packages from the boot class path)
• Imported packages
• Required bundles
• The bundle's class path (private packages)
• Attached fragments

30. OSGi Module System - Summary
- Promotes a better structuring of your application code by
defining clear boundaries
- Robust class loading model that overcomes the deficiencies of
the conventional Java
- Versioning control
- Lifecycle
- Modularization is rewarded when creating new systems and
modifying existing ones
- No silver bullet, bad code and bad ideas are still bad

31. What else is missing?

32. Service-Oriented-Architecture
- OSGi introduces service layer as primary means of collaboration
between bundles
- Lightweight implementation
No protocols, no stubs - direct Java method calls
- Service Registry is where decoupling between provider and
consumer happens

33. Services
Services
- Services are identified with bundles
- Registered and looked up using their interface name
Follow publish/find/bind model
- Used as bundle’s input/output ports
- Allow loose coupling between modules – modules can be substituted
Allow lazy instantiation and late binding
Meta-data is decoupled from implementation
- Service properties can be queried without the need for creating
service instance

34. Services (2)
But most importantly, services are dynamic
- Static dependencies are handled by the module layer,
runtime dynamics are realized through services
-Services can be enabled/disabled/substituted dynamically at runtime
However, there is a challenge
- Fully dynamic systems require a different way of thinking
Services may come and go at any moment in time
Multiplicity of service providers

35. OSGi Implementations
Several independently implemented OSGi frameworks exist today,
including four that are available as open source software
o Equinox - the most widely deployed OSGi framework today owing to its
use in the core runtime of Eclipse. It is also the official RI (Reference
Implementation) of the OSGi spec.
o Knopflerfish - popular and mature implementation of both OSGi Release
3 and 4.1. It is developed and maintained by Makewave AB
o Apache Felix - a community implementation of the OSGi Release 4.x.
It is designed particularly for compactness and ease of embedding, and is
the smallest (JAR size ~360K) implementation
o Concierge - a very compact and highly optimized implementation of
OSGi Release 3. This makes it particularly suited to resource-constrained
platforms such as mobile phones.

36. Apache Karaf
• Birthdate - 16th of June 2010
• Platform running on OSGI (Apache Felix, Eclipse
Equinox)
• Provides a lightweight container where
• Applications, Integration projects, Web Service, JMS Brokers, Java
applications can be deployed
• Used by ServiceMix, Geronimo projects

37. Karaf: an OSGi container
Karaf is a small OSGi based runtime which provides a
lightweight container onto which various components and
applications can be deployed.

38. Supported Karaf features
• Hot deployment
• Dynamic configuration
• Provisioning
• Native OS integration
• Extensible Shell console
• Remote access
• Security framework
• Managing instances

39. Karaf structure: Important Files and Folders
+---bin: Startup scripts and commands
+---data: Karaf work directory
| +---cache: Installed bundles
| +---log: Default log directory
| +---tmp: Temporary files
+---deploy: Directory for file system deployment
+---etc: Configuration files
+---instances: Instance management
+---lib: Core libraries
+---system: System bundle repository

40. Command line

41. Command Groups (Karaf 3.x)
• bundle:* - Install and control bundles
• dev:* - Development support
• feature:* - Manage features
• instance:* - Control of multiple instances
• jaas:* - JAAS role and rights management
• log:* - Log display
• service:* - Manage OSGi Services
• shell:* - Useful helper functions (i.e. grep, more, info)
• ssh:* - SSH connections
• system:* - OSGi framework management

42. Custom Commands
• Add custom commands from your bundles
• Extend org.apache.karaf.shell.console.OsgiCommandSupport
• Add @org.apache.karaf.shell.commands.CommandAnnotation
• Register command via Blueprint

43. Remote Management
• Use command line via SSH:
ssh-p 38031karaf@karaf-mydomain.paasplus.com
• Configuration via: org.apache.karaf.shell.cfg
• User and Role management via JAAS
• Configure via users.properties
• org.apache.karaf.command.acl.* for command specific
permissions

44. Deployment
Deployment of:
• Bundles
• Blueprint files (xml)
• Features
• Kar Archives
• „plain“ jarfiles

45. Maven deployment
Deploy via any Maven repository
• Bundles
• Features
• Configurations
Add additional repos to org.ops4j.pax.url.mvn.cfg
Install features or bundles

46. Features

47. Configuration Admin
Configuration can change at any time and you're expected
to react to these changes;
Bundles will be notified of new, updated, and removed
configuration data.

48. Karaf & Spring
Karaf has its own Dependency Injection API: Blueprint
Blueprint is a standard defined in OSGi that allow bean
definition, service definition and dependency injection
Using Spring Dynamic Module we can also use Spring in
Karaf.
SpringDM explores bundles and load Spring xml files
Spring DM allows you to interact with the world without using
OSGi API in our code: in this way the code is cleaner and
classes that we write (our modules) can be reused on other
platforms.

49. Blueprint
• Blueprint - dependency injection framework for OSGi.
• Handles the wiring of JavaBeans, and instantiation and
life cycle of an application.
• Blueprint is expressed as an XML file.
Blueprint will be expressed as a top-level element:

50. Blueprint example

51. Karaf & Web
Pax Web allows Karaf to support web. Using integrated Web
Server Jetty, it implements:
HTTP Service API defined in OSGi
Web Application API defined in OSGi Enterprise
Like Spring DM, Pax Web explores Bundles installed in Karaf
to find web.xml files.
When it finds it, Pax Web starts application by creating
servlets, filters and initializing servlet context defined in web
deployment descriptor.

52. Web Applications
• Webapp support via Pax Web feature
• Integrated Jetty
• etc/jetty.xml
• OSGi http Service (Whiteboard pattern)
• Register Web application resources as OSGi services
• Full Webapp
• Deploy war or wab
• CDI support
• Commands
• web:list, stop, start (Webapps)
• http:list (Servlets)

53. Web console
A modular web console for managing your Java
stuff

54. Pax-Exam testing framework
Automated Testing Framework
Automates:
• Set up the environment and initial options for the OSGi container
• Start the OSGi container
• Install the prerequisite bundles into the OSGi container
• Install and run the test classes

55. Cellar Clustering
• Cluster solution for Apache Karaf
• Based on Hazelcast
• Support for different topologies
• Synchronization of deployments and configurations
• Cross-Node Event publishing

56. How can you use OSGi within your
existing applications?
Bundling existing code
- Start with your existing application
and all its dependent jars
- Create a bundle activator (i.e.: the
existing startup class or main) if
needed
- Put all libraries into one bundle
Super sized!
Don’t worry, it’ll get better
- Having a working bundle (whatever
the size) is a good baseline and
allows for gradually replacing the
dependent jars with bundles
- Keep it working!

57. Markets & Solutions
Automotive: BMW, Volvo, Bombardier…
Smart Home: Bosh, Siemens, Phillips…
E-Health: Siemens Med…
Enterprise
o Currently the OSGi framework is adopted by most
enterprise Java vendors for internal use as the underlying
infrastructure platform
o Base for the new application server generation architecture
o Oracle BEA mSA – micro-service architecture built on OSGi is the base for BEA products
o JBoss MicroContainer - replaces old JMX MicroKernel
o IBM WebSphere, Lotus as well as other ~200 products run on Equinox
o JOnAS, SpringSource DM server…
o Smaller vendors, such as SpringSource and Paremus, as well as open source projects such as
Apache ServiceMix and Apache Aries, are starting to promote the direct use of the OSGi
programming model in developing enterprise applications, and some early adopters such as
LinkedIn and VMware have started to do so

58. OSGi benefits
• You can install, uninstall, start, and stop different modules
of your application dynamically without restarting the
container.
• Your application can have more than one version of a
particular module running at the same time.
• OSGi provides very good infrastructure for developing
service-oriented applications, as well as embedded,
mobile, and rich internet apps.

59. Thank You
Quations?