Subsystems is an OSGi Alliance specification that standardizes the development and deployment of bundle collections. The specification was motivated by the need for bundle collections exhibited by many existing products & projects, including: Apache Karaf, Apache Aries, Eclipse Virgo, WebSphere Application Server, etc. Three different types of collections are defined in the specification: feature, composite & application, each having different rules covering sharing of packages and services, and each being designed with different use cases in mind. Subsystems was first introduced in OSGi Enterprise R5 and since then work has continued on further enhancements. This talk will introduce the Subsystems specification, describe some practical use cases, provide demonstrations based on the Apache Aries Reference Implementation, and finally talk a bit about what's coming in the next version. Bio: Graham Charters is a Senior Technical Staff Member in the IBM WebSphere Application Server development organization. He is responsible for the OSGi Applications feature of the Application Server and a committer and PMC member of the Apache Aries OSGi programming model project. He is also the IBM technical lead in the OSGi Alliance Enterprise Expert Group.

1. © 2014 IBM Corporation
OSGi DevCon 2014Wednesday, June 11, 2014
SUBSYSTEMS IN THE WILD
Graham Charters
Senior Technical Staff Member
IBM
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2. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Contents
• Motivation
• Subsystems Overview
• Use case “In the Wild”
…with a demo or two along the way
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3. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Motivation
• Many Enterprise Java platforms offer
bundle collections
• Apache Aries – Applications
• Apache Karaf – Features
• Eclipse Virgo – Plans, PARs
• WebSphere – OSGi Applications,
Composite, Features
• Oracle GlassFish – Applications
• Paremus Service Fabric – System Parts
• Standardization enables
• Portability
• Tools
• Ecosystem
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4. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Subsystem Concepts
• A Grouping Resources (Bundles)
• An Identity
• Scoping for visibility
• Group Management
• Documentation (coming in 1.1)
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5. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Subsystem Types
• Subsystem types aligned with common sharing policies
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Type Sharing Policy
Feature Share everything
Application Share everything in, share
nothing out
Composite Explicit selective sharing

6. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Feature Subsystems
• A grouping of related artefacts
• Simplifies re-use &
provisioning
• Raw resources in the runtime
• Useful for frameworks &
libraries
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Bundle A Bundle B
Bundle C Bundle D
Feature A Feature B

7. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Feature A
Application Subsystems
• Isolated group of related
artefacts
• Share nothing out
• Implicitly share all in
• Useful for independent
applications in same process
• cheap/weak multi-tenancy
• Can share common
infrastructure
• e.g. frameworks or libraries
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Bundle A Bundle B
Bundle C Bundle D
Application A Application B
✘
✘

8. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Composite Subsystems
• Isolated group of related
artefacts
• Explicitly share in
• Explicitly share out
• Useful for controlling
coupling of “subsytems”
(hide internals)
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Feature A
Bundle A Bundle B
Bundle C Bundle D
Composite A Composite B
✘
✘

9. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Nesting
• Subsystems can be nested
• All subsystems are
descendants of the “Root
Subsystem”
• Enables runtime subsystem
‘sharing’
• Enables logical groupings
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Feature
Bundle A Bundle B
Bundle D
Application
Root
Bundle C

10. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Definition
• Subsystem manifest format
• Jar manifest without the annoying restrictions
• Familiar to bundle programmers
• Configuration by exception
• Can be left out altogether
• Version ranges enabled deployment flexibility
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Subsystem-ManifestVersion: 1.0
Subsystem-Name: HttpService
Subsystem-Description: This feature enables the http service
Subsystem-SymbolicName: com.acme.httpService
Subsystem-Version: 1.0.0
Subsystem-Type: osgi.subsystem.feature
Subsystem-Content: httpServiceWab;version="1.0.0",
org.eclipse.equinox.http.servlet;version="1.1.200",
org.eclipse.osgi.services;version="3.3.0"

11. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Packaging
• Zip file with .esa extension
• Optionally contains resources
(bundles) for provisioning
• duplicates binaries
• bloats deployment
• inhibits update
• does not influence runtime
sharing
• uses repositories if not
• Optionally contains
Subsystem manifest
• defaulted if not
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Subsystem.esa
Bundle A
Bundle C
Bundle B
Bundle D
Subsystem.MF

12. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Management
• Subsystem service
• Introspection of subsystem
• Lifecycle management of
subsystem
• Management of child
subsystems (e.g. install)
• Roots subsystem – solves
the bootstrap problem
• Really only for systems
programmers – runtimes
should simplify management
capabilities
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Feature A
Bundle A Bundle B
Bundle C Bundle D
Application A Application B
Root

13. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Repositories
• Repositories represent
collections of resources
considered during
provisioning
• The Subsystem archive
contents
• Simplifies operations, bloats
deployment
• The visible set of installed things
• Configured repository services
• Enables single binary for install and
service
• Fits well with ‘continuous delivery’
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Subsystem.esa
Bundle A
Bundle C
Bundle B
Bundle D
Subsystem.MF
Feature
Bundle A Bundle B
Bundle D
Application
Bundle C
Bundle A
Bundle C
Bundle B
Bundle D

14. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Dependency Management
• Installs missing
dependencies
• Removes redundant
dependencies
• Dependency installation
maximises runtime sharing
• Dependency types
• Package
• Services via declarative
models (optional)
• Require-Capability
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Bundle A Bundle B
Feature
Bundle C
Bundle D
Application Composite

15. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
From Test to Production
• Product deployment
resolution uncertainty
• Deployment manifests lock
down deployment
• Repository and install
governance necessary for
guarantees
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Subsystem.esa
Bundle A
Bundle C
Bundle B
Bundle D
Subsystem.MF
Deployment.MF

16. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Extenders and whiteboards
• Extender & whiteboard patterns
commonplace
• Rely on visibility of bundle &
service lifecycle events
• Subsystem scoping can hide
these events from extenders
• The System Bundle is your friend
• Sees all events
• Can be found by any bundle using
its location string
• Use this to register trackers
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Bundle
Service
Bundle systemBundle =
bc.getBundle(org.osgi.framework.Constants.SYSTEM_BUNDLE_LOCATION);

17. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Demo
• httpservice:
http service
whiteboard
• greenWeb,
redWeb:
register http
services
• wab-1.0: web
container
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wab-1.0
WebContainer
Impl
WebContainer
API
Root
(kernel)
greenWab
greenWeb
redWab
redWeb
httpservice
httpServiceWab http.servlet
osgi.services
“User”

18. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
In the Wild
• Confession time…
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19. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Reuse/release equivalence principle
• The unit of reuse is the unit of release
• A matter of perspective; jar, library, framework, product
• Higher levels take on ‘product’ qualities
• Licensing
• Documentation
• Install
• Subsystems 1.1 adds many headers for product qualities
• Icons, Docs, License, Localization
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20. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Use Case
• Decomposition of a product into re-usable capabilities
• Independent release of product capabilities
• Users care about capabilities, not implementation
• Users want to consume capabilities piecemeal
• ‘Stack’ products re-use subset of capabilities
• ‘Stack’ products add their own capabilities
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21. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Subsystem Asset Life-cycle
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Dev,
build,
test
Provision
Feature A
Bundle A Bundle B
Bundle C Bundle D
Application A Application B
Root
Install
W.esa X.esa
Y.esa Z.esa
Repository &
Resolver Services
Z.esa
Y.esa
X.esa
Release
Repository
X.esa
Doc, license, icon, etc
Repository &
Resolver
Services

22. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Demo
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23. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Summary
• The standard way to manage groups of resources
• Subsystem ‘types’ defines sharing for most common use
cases
• Deployment resolution enables sharing of runtime
resources
• Repositories-based resolution enables sharing of binaries
• New 1.1 features enable more ‘product’ and marketplace-
like qualities
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24. © 2014 IBM Corporation
OSGi DevCon 201411 June 2014
Find out more
• Reference Implementation:
• Subsystems 1.0
https://svn.apache.org/repos/asf/aries/trunk/subsystem/
• Subsystems 1.1
https://svn.apache.org/repos/asf/aries/branches/subsystemsR6/subsystem/
• New Early Draft Specification of OSGi Enterprise Release 6
• http://www.osgi.org/Specifications/Drafts
• New OSGi Core Release 6 Specification
• http://www.osgi.org/Specifications/HomePage
• OSGi Alliance Design Documents
• https://github.com/osgi/design
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