OSGi Community Event 2018 Presentation by David Bosschaert (Adobe) Abstract: OSGi lends itself well to develop extensible applications assembled from reusable modules, where a set of bundles together with a set of configurations deployed to a provisioned OSGi framework is the application. While this works very well for the originally intended use-cases, maintaining and building large applications developed by multiple teams often requires to assemble multiple larger components for which there is limited support in OSGi as of today. This is especially true in cases where multiple groups of bundles, configuration, metadata, and other artifacts need to be combined. In this talk we will introduce you to OSGi RFP-188, named OSGi Features, which defines the requirements on providing a solution. We'll establish a shared understanding of the problem space and how it relates to already available mechanisms in OSGi (like e.g. subsystems, deploymentadmin, startlevels, etc.) and will subsequently, review it in the context of some of the current (open source) solutions like Apache Karaf Features and Apache Sling Features and Bnd.

1. Feature Model, Where Art Thou?
David Bosschaert & Karl Pauls – Adobe

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David Bosschaert
§ Senior Computer Scientist @ Adobe
§ Member of the Apache Software Foundation
§ OSGi Enterprise Expert Group co-chair
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3. © 2018 Adobe Systems Incorporated. All Rights Reserved. Adobe Confidential.
Karl Pauls
§ Computer Scientist @ Adobe
§ Member of the Apache Software Foundation
§ PMC Member of Apache Felix and Sling (VP Apache Felix)
§ Co-Author OSGi in Action
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Agenda
§ Requirements
§ Model
§ Building Blocks
§ Demo
§ Outlook
§ Q & A
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5. Requirements

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Why the Feature Model
§ Provisioning model, but then better
§ Focus on the Architect, Designer
§ Requirements at Sling
§ Prototype maturing
§ …Karaf, Eclipse, Subsystems, Bnd…
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Requirements
§ Easily authorable via text file
§ 1:1 mapping of File ⇠⇢ Feature
§ Declarative Requirements and Capabilities
§ Inheritance
§ API Whitelisting
§ Extensible format
§ Compose an application
[1] https://github.com/apache/sling-org-apache-sling-feature/blob/master/requirements.md
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Feature Files
§ JSON
§ ID
§ Variables
§ Bundles
§ Configurations
§ Capabilities, Requirements
§ Custom Content
§ Can be published in Maven
§ Tooling and Runtime support in Sling, others can support too
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9. Model

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Features
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{
"#": "A key that starts with a hash is a comment",
"id": "org.apache.sling:my.app:feature:optional:1.0",
"variables": {
"cfgvar": "somedefault",
"xyz-ver": "1.2.3"
},
"framework-properties": {
"foo": 1,
"org.osgi.framework.storage": "${tempdir}",
"org.apache.felix.scr.directory": "launchpad/scr"
},

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Features (cont.)
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"configurations": {
"my.pid": {
"foo": 5,
"bar": "${cfgvar}",
"# The tempdir variable is not specified at the variables section.":
"# It needs to be provided at launch, otherwise the launch will stop.",
"tempdir": "${tempdir}",
"number:Integer": 7
},
"my.factory.pid~name": {
"a.value":"yeah"
}
}

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Feartures (cont.)
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"bundles": [
{
"id": "org.apache.sling:security-server:2.2.0",
"#": "This is the relative start order inside the feature",
"start-order": 5
},
{
"id": "org.apache.sling:another-bundle:2.1.0",
"#": "OSGi start level is also supported",
"start-level": 20,
"configurations": {
"#": "This configuration only gets applied when this bundle is resolved",
"org.apache.sling.somepid": {
"dbuser": "${dbuser}",
"dbpass": "${dbpass}"
}
}
}
],

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Features (cont.)
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"includes":
{
"id": "org.apache.sling:sling:9",
"removals": {
"configurations": [],
"bundles": [],
"framework-properties": []
}
}

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Features (cont.)
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"requirements": [
{
"namespace": "osgi.contract",
"directives": {
"filter": "(&(osgi.contract=JavaServlet)(version=3.1))"
}
}
],
"capabilities": [
{
"namespace": "osgi.implementation",
"attributes": {
"osgi.implementation": "osgi.http",
"version:Version": "1.1"
},
"directives": {
"uses": "javax.servlet,javax.servlet.http,org.osgi.service.http.context"
}
}
],

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OSGi Framework
API Whitelisting with Regions
Bundle
Bundle
Bundle
Product
User
Bundle
Global Region
Product Exported Packages:
com.product.api
org.apache.sling.api
Internal Product Region
Packages:
com.product.commons
exports imports
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Product Exported Packages:
com.product.api
com.product.commons
org.apache.sling.api

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Custom Metadata
§ Features can contain custom metadata
§ Text, JSON, or Artifact (IDs)
§ Processed by plugins on feature merge and execution
§ Default provided for repoinit and content-packages
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"repoinit:JSON|true":[
"create path (sling:Folder) /libs",
"create path (sling:Folder) /apps”
]
,
"content-packages:ARTIFACTS|true":[
”org.apache.sling:org.foo.bar:zip:0.0.34”
]

17. Building Blocks

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Develop and publish feature models
Feature
Models
Analyser
slingfeature
-maven-
plugin
Maven
Repository
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Create a Running System
Feature
Models
Maven
Plugin
Final system
feature Launcher
Running
system
Maven
Repo/Cache
Resolver
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20. Building Blocks Applied

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Sling Feature Maven Plugin
§ Attach features in src/main/features as “.slingosgifeature”
§ org.apache.sling:slingfeature-maven-plugin:0.2.0-SNAPSHOT
§ New packaging type slingosgifeature
§ When <extensions>true</extensions>
§ attach-features
§ Attach feature files found in the project to the projects produced artifacts. This includes features found
in src/main/features as well as features produce with the aggregate-features goal.
§ aggregate-features
§ Produce an aggregated feature from a list of features (a.k.a composition)
§ repository
§ Produce a local maven-structure cache with all artifacts referenced in specified features
Documentation at https://github.com/apache/sling-slingfeature-maven-plugin

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Launcher
Usage: .... -D <arg> Set framework properties
-dao <arg> Only download required artifacts into directory
-f <arg> Set feature files
-fv <arg> Set felix framework version
-p <arg> Set home dir
-u <arg> Set repository url
-V <arg> Set variable value
> java -jar org.apache.sling.feature.launcher-0.1.0-SNAPSHOT.jar –f mvn:org.apache.sling/my.feature/1.0.0
Handlers for extension merging as well as extension execution as ServiceLoader services via
classpath
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23. Demo
code at: https://github.com/bosschaert/example-featuremodel

24. Outlook + Summary

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Outlook
§ API Whitelisting
§ Resolver
§ Minimal Docker Containers
§ OSGi Specification process, Enterprise Expert Group RFP 188 (https://github.com/osgi/design)
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Images licensed from Adobe Stock (https://stock.adobe.com)

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Evaluate the Sessions
-1 0 +1
Sign in and vote at eclipsecon.org
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27. Q&A

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Acknowledgements
§ Why the feature model picture by shootforalivi35 licensed from Adobe Stock https://stock.adobe.com
§ Outlook background picture by volgariver licensed from Adobe Stock https://stock.adobe.com
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