Building Modular Enterprise Applications - C Ziegeler

© 2014 Adobe Systems Incorporated. All Rights Reserved.
Building Modular Enterprise Applications
Carsten Ziegeler | Adobe Research Switzerland
1

About
carsten.ziegeler@adobe.com @cziegeler
§  RnD Team at Adobe Research Switzerland
§  Member of the Apache Software Foundation
§  Apache Felix and Apache Sling (PMC and committer)
§  And other Apache projects
§  OSGi Core Platform and Enterprise Expert Groups
§  Member of the OSGi Board
§  Book / article author, technical reviewer, conference speaker
2

Motivation
§  Enjoy the power of modularity
§  OSGi is everywhere
§  From embedded systems to enterprise applications and THE CLOUD
§  Adapting a technology is always a challenge
§  Common pitfalls
§  Potential solutions
3

But wait a second…
§  Adobe & OSGi ?
4

But wait a second…
§  Adobe & OSGi ?
5

Adobe & OSGi & Open Source & Open Development
§  Using OSGi in various products
§  Strategic member of the OSGi Alliance
§  Board of directors
§  Participating in CPEG and EEG
§  Highly contributing to open source
§  Especially Apache Software Foundation
§  Participating in open standards
§  Embracing open development
6

Case Study: The Development of Adobe Experience Manager
7

Back to the Future: Web Content Management Code History
8

Back in the Days…CQ 4
9

OSGi based Enterprise Web Content Management – Adobe CQ5
10

Adobe Experience Manager
11

Motivations for Going Modular (2006)
§  Aged code base
§  Monolithic
§  Highly entangled
§  Growing complexity and functionality
§  No clear separation between API and implementation
§  Increasing customer base
§  Team growth
12

Modularity is Key
§  Manage growing complexity
§  Support dynamic extensibility
§  Define contracts between modules
13

Potential Solutions (2006)
§  Spring?
§  OSGi?
§  Other open source component frameworks?
§  DIY?
14

Benefits of OSGi
§  OSGi modules = bundles
§  jars with strict enforcements
§  Exported packages with version
§  Imported packages with version range
§  Private packages
§  Service Registry
§  Separation of Concerns
§  Loose coupling
15

Modularity - How do we get there? (2006)
§  Start with a single big bundle?
§  Embedding OSGi framework?
§  Complete rewrite?
16

The Fun Way : Complete Rewrite
§  New architecture
§  New backend (Apache Jackrabbit)
§  New web application framework (Apache Sling)
§  New UI
§  Build modules from the start
§  Control evolution
§  (Provide tools for migration from old solution)
17

OSGi and Open Source (2006)
§  Apache Felix
§  Equinox
18

Framework runs and now?
§  We need bundles!
§  Build tools
§  Ant? (BND)
§  Maven? (Apache Felix Maven Bundle Plugin)
19

Maven Bundle Plugin (2007)
§  Specifying all OSGi metadata in the POM
§  Exported packages
§  Imported packages and versions get calculated
§  Parent POM to define rules for bundle symbolic name
20

Maven Bundle Plugin – First problems
§  Exported package version = POM version
§  New private package needs updating the pom
§  Slight diﬀerence in version handling between OSGi and Maven (The SNAPSHOT problem)
§  2.0.1 < (OSGi) 2.0.1-SNAPSHOT < (Maven) 2.0.1
§  Semantic versioning?
21

Excursion on Versioning
§  Marketing Versions vs. Engineering Versions
§  Versioning Package Exports
§  Engineering Versions
§  Apply versions !
§  Semantic Versioning crucial
§  Bundle Versions
§  Grey area
§  Semantic Versioning helpful
§  Application Versions
§  Marketing Versions
22

Versioning Best Practice
§  Package Exports
§  Always apply a version to package exports
§  Start with 1.0
§  Only increment when changing the API
§  Think hard before increasing the major version !
§  Package Imports
§  Ensure proper version range import
23

Semantic Versioning
§  Nice whitepaper on the OSGi homepage
§  Versioning policy for exported packages
§  OSGi versions: <major>.<minor>.<micro>.<qualifier>
§  Updating package versions:
§  Fix/patch (no API change) : update micro
§  Extend API (aﬀects implementers, not clients) : update minor
§  API breakage: update major
24

Versioning Annotations
§  BND or new with OSGi R6
§  Annotations for documenting semantic versioning information
§  @Version
§  @ProviderType
§  @ConsumerType
25

Versioning Best Practice (cont.)
§  Bundle Versions
§  Always use and manage bundle version
§  Align bundle version with Maven version
§  Use odd micro versions for SNAPSHOTs
§  e.g. 0.0.1-SNAPSHOT, 1.3.5-SNAPSHOT
§  Use even micro versions for release
§  e.g. 1.0.0, 1.3.6
§  Dependencies
§  Always use least required version for dependencies
26

Maven Bundle Plugin – Today
§  Parent POM to define rules for bundle symbolic name and private packages
§  No package versioning information in POM (annotations)
§  Follow semantic versioning
§  Odd/even versioning policy
§  Usually no OSGI metadata in the POM
27

What about Components and Services (2007)?
§  Framework API is usually too low level
§  Make development as easy as possible
§  Try to hide dynamics
§  And there are OSGi compendium specs
§  Declarative Services
§  Configuration Admin
§  Metatype
28

Component Development with Declarative Services
§  Declarative Services (OSGi Compendium Spec)
§  Defines Service Component Runtime (SCR)
§  Declarative component model
§  XML descriptor for components including
§  Provided services
§  References to other services
§  Configuration properties
29

Configuration Admin
•  OSGi Configuration Admin
•  “The” solution to handle configurations
•  Configuration Manager
•  Persistence storage
•  Service API to retrieve/update/remove configuration
•  OSGi Metatype Service
•  Description of bundle metadata
•  Description of service configurations
•  Property type, name, and description
30

What about Components and Services (2007)?
§  Framework API is usually too low level
§  And there are OSGi compendium specs
§  Declarative Services
§  Metatype
§  No (Apache) open source implementations available
§  Nearly no tooling
§  Declarative Services uses XML descriptors
§  Metatype uses XML descriptors and property files
31

DIY – Donations to Apache Felix
§  Apache Felix SCR (Declarative Service Implementation)
§  Apache Felix Config Admin
§  Apache Felix Metatype
§  Apache Felix Preferences
§  Apache Felix SCR Tooling
§  Java annotations for generating DS and Metatype descriptors
§  Maven, ANT, BND
32

§  Declarative Services (OSGi Compendium Spec)
§  Defines Service Component Runtime (SCR)
§  Apache Felix SCR Annotations (DS annotations)
§  Some advantages (in combination with the tooling)
§  POJO style
§  Declarative
§  Single source: just the Java code, no XML etc.
§  "Integration" with Configuration Admin and Metatype Service
33

Components and Services with OSGi
§  Service interface
§  Public (if exported for other bundles)
§  Versioned through package version (Semantic versioning)
§  Private for internal services (sometimes useful)
§  Component / service implementation
§  Always private
34

My First Component
35
package com.adobe.osgitraining.impl;

import org.apache.felix.scr.annotations.Component;

@Component
public class MyComponent {

}

Component Lifecycle
36

import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Deactivate;

@Component
public class MyComponent {

@Activate
protected void activate() {
// do something
}

@Deactivate
protected void deactivate() {
// do something
}
}

Providing a Service
37

import org.apache.felix.scr.annotations.Service;
import org.osgi.service.event.EventHandler;

@Component
@Service(value=EventHandler.class)
public class MyComponent implements EventHandler {

…

Using a Service
38


@Component

@Reference
privateTThreadPool threadPool;

…

Using an Optional Service
39


@Component

@Reference(cardinality=ReferenceCardinality.OPTIONAL_UNARY,
policy=ReferencePolicy.DYNAMIC)
private volatileTThreadPool threadPool;

@Reference(cardinality=ReferenceCardinality.MANDATORY_UNARY)
privateTDistributor distributor;

Component Properties -> Service Properties
40
import org.apache.sling.commons.osgi.PropertiesUtil;

@Component
@Properties({
@Property(name="service.vendor", value="Who?”),
@Property(name="service.ranking", intValue=500)
})
public class DistributingEventHandler
implements EventHandler {

Configuration Admin
•  OSGi Configuration Admin
•  “The” solution to handle configurations
•  Configuration Manager
•  Persistence storage
•  Service API to retrieve/update/remove configuration
•  Integration with Declarative Services
•  Configuration changes are propagated to the components
•  Configurations are stored using the PID
41

Configuration – Supports Configuration Admin
§  Provided map contains
§  Configuration properties from Configuration Admin
§  Defined component properties
42

@Activate
protected void activate(final Map<String, Object> props) {
…
}

Configuration – Supports Configuration Admin
43

@Component
@Properties({
@Property(name="event.topics", value="*", propertyPrivate=true),
@Property(name="event.filter", value="(event.distribute=*)",
propertyPrivate=true)
})

private static final int DEFAULT_CLEANUP_PERIOD = 15;

@Property(intValue=DEFAULT_CLEANUP_PERIOD)
private static final String PROP_CLEANUP_PERIOD ="cleanup.period";

private int cleanupPeriod;

@Activate
protected void activate(final Map<String, Object> props) {
this.cleanupPeriod =
PropertiesUtil.toInteger(props.get(PROP_CLEANUP_PERIOD));
}

Configuration Update
44
import org.apache.sling.commons.osgi.OsgiUtil;


…

@Modified
protected void update(final Map<String, Object> props) {
this.cleanupPeriod =
PropertiesUtil.toInteger(props.get(PROP_CLEANUP_PERIOD));
}
Without @Modified:
Component is restarted on config change!

Metatype
§  OSGi Metatype Service
§  Description of bundle metadata
§  Description of service configurations
§  Property type, name, and description
45

Configuration – Supports Metatype
46

@Component(metatype=true, label="Distributing Event Handler",
description="This handler is awesome.")

@Properties({
@Property(name="event.topics", value="*", propertyPrivate=true)
})

private static final int DEFAULT_CLEANUP_PERIOD = 15;

@Property(intValue=DEFAULT_CLEANUP_PERIOD,
label="Cleanup Period",
description="This is the cleanup period in seconds.")
private static final String PROP_CLEANUP_PERIOD ="cleanup.period";

§  Straight forward component development
§  Single source of truth
§  (Will even be easier with new Declarative Service spec from R6)
§  Typical problems
§  OSGi dynamics is hidden
§  Handling references of cardinality multiple
§  Copying of bad practices
47

And what about THE WEB? (2007)
§  OSGi Http Service Specification
§  Based on servlet API 2.1
§  Programmatic API to register servlets and resources
§  Apache Felix HTTP implementation
§  Later whiteboard support in Apache Felix implementation for
§  Servlets
§  Filters
§  Some listeners
48

And what about THE WEB?
§  OSGi Http Service Specification
§  Based on servlet API 2.1
§  Programmatic API to register servlets and resources
§  Apache Felix HTTP implementation
§  Invented Apache Sling Web Framework
§  Resource based approach
§  Scripting
§  Written as OSGi bundles
§  Later whiteboard support in Apache Felix implementation for
§  Servlets
§  Filters
§  Some listeners
§  New OSGi Http Whiteboard Service Spec in R6
49

But what about Provisioning and Deliverables? (2007)
§  Wishes
§  Single definition of deliverable (bundles, configurations, proprietary packages)
§  Diﬀerent flavors: web application, standalone
§  Easy and flexible updates
50

But what about Provisioning and Deliverables? (2007)
§  Wishes
§  Single definition of deliverable (bundles, configurations, proprietary packages)
§  Diﬀerent flavors: web application, standalone
§  Easy and flexible updates
§  No open source solution available
51

Contributing Apache Sling Launchpad Ecosystem
§  Creating a distribution is easy
§  Standalone jar file and/or web application
§  Maven Launchpad Plugin
§  Define bundle list
§  Add other artifacts
§  Configurations
§  Leverages Apache Sling’s OSGi installer
52

Bundle List Example
53
<?xml version="1.0"?>
<bundles>
<startLevel level="boot">
<bundle>
<groupId>org.apache.sling</groupId>
<artifactId>org.apache.sling.commons.log</artifactId>
<version>2.1.2</version>
</bundle>

…

<startLevel level="9">
<bundle>
<groupId>org.apache.felix</groupId>
<artifactId>org.apache.felix.eventadmin</artifactId>
</bundle>

…

<startLevel level="0">
<bundle>
<groupId>org.some.company</groupId>
<artifactId>a.strange.artifact</artifactId>
<type>zip</zip>
</bundle>

Apache Sling Launchpad
§  Bootstrap code
§  Includes Apache Felix
§  Handles framework updates
§  Launch an OSGi framework
§  Standalone jar with http service
§  As a web application with http bridge
§  Deploy packaged artifacts
§  Configurable
§  sling.properties
§  (system properties / servlet parameters)
54

OSGi Standalone App or OSGi Webapp with Launchpad
55
JAR File
Launchpad Main
Bootstrap Code
OSGi Framewok
OSGi HTTP Service
sling.properties
Deployable Artifacts
WE
I
R
N
IR
JO
S-
H
BA
B
G
S
EL
@AD
OBE
WAR File
Launchpad Servlet
Bootstrap Code
OSGi Framewok
HTTP Bridge / OSGi HTTP Service
sling.properties
Deployable Artifacts
WE
I
R
N
IR
JO
S-
H
BA
B
G
S
EL
@AD
OBE

Apache Sling OSGi Installer
§  General service covering
§  Install
§  Update
§  Uninstall
§  Of
§  Bundles
§  Custom artifacts
56

Apache Sling OSGi Installer
57
OSGi Installer
File Provider
JCR Provider
Launchpad Provider
Providers Transformers and Task Factories
Config Admin
Bundles
Add/Remove
Update
Artifact
Artifact
Transformed
Artifact
State &
Artifact DB

Advantages of the OSGi Installer Family
§  Pluggable and highly customizable
§  New artifact types: transformer + task factory
§  New artifact sources: provider
§  Batch handling
§  Retry mechanism in the installer core
§  Bundle installation order doesn’t matter
§  State management in the installer core
§  Defined workflow
§  Copes with 3rd party changes
58

Running Deliverables and what about administration? (2007)
§  Nothing really available in the open source world
§  Especially not web based
59

Donating Apache Felix Web Console + Plugins
§  Rich set of core functionality
§  Bundles
§  Services
§  System Information
§  (JQuery based UI)
§  Extensible
§  Pluggable authentication
§  Still light-weight
§  REST interface
60

Web Console Demo I
61

Web Console Demo II
62

Web Console Demo III
63

Web Console - Oﬄine Usage
§  Status zip contains
§  Output from all inventory printers
§  Output from special web console plugins
§  Attachments
§  JSON files
§  Automated analysis
§  Bundle list and status
§  Log files
64

Problems solved…
§  Modularity
§  OSGi bundles
§  Semantic versioning
§  Services and components
§  Development
§  Frameworks and tooling
§  Deliverables and provisioning
§  Administration
65

Hitting the Real World – 3rd Party Libraries
§  Use them as bundles
§  Project delivers already a bundle
§  Apache Commons, Apache Sling etc.
§  Use special bundle repositories
§  Apache Felix Commons, Spring etc.
§  But check included metadata!
§  Create your own wrapper
§  Easy with the Felix maven bundle plugin
§  Include classes in your bundle
§  Again: easy with the Felix maven bundle plugin
§  Convince the projects to provide useful OSGi metadata!
66

Hitting the Real World – "Enterprise" Requirements
§  Testing under high load / high concurrency
§  Reimplementing some (open source) modules
§  Not every developer is aware that code can be called concurrently
§  And how to solve this in an acceptable way
§  Dynamic nature of OSGi
§  Relatively painless with DS and annotations
§  Gets trickier with plain framework API and/or cardinality multiple
§  Again: concurrency
67

Hitting the Real World – All Time Favorites
§  When is my system ready?
§  Diﬀerent strategies
§  All bundles started and specific start level reached
§  Special startup handler service for notification (Apache Sling)
§  Fighting against FUD
§  OSGi is slow, consumes too much memory, complicated,
§  has no dependency injection, is not used in the enterprise…
68

Additional Challenges
§  Clustering
§  Discovery
§  Distributed Eventing
69

On the Roadmap
§  OSGi subsystems
§  Grouping of bundles
§  Export / import boundaries on subsystem level
§  OSGi Remote Services
§  OSGi Asynchronous Services
§  OSGi Distributed Eventing
70

Think Modular…
•  This is not a new concept or latest hype!
•  Think about modularity!
•  Create a clean package space
•  What is your API?
•  public vs private
•  Make things only public if necessary/used
•  Starting with private stuﬀ going public is easy
•  Use proper versioning contracts
•  Semantic Versioning
71

…Be Modular!
•  Provide bundles
•  Add manifest information
•  Think about dependencies
•  Additional bundle vs include
•  Optional
•  Version ranges
•  Manage releases and versions properly
•  Benefits even without OSGi
72

Component Development
§  Contract defined by service interface
§  Declarative Services is a powerful component model
§  Minimal OSGi knowledge required with available solutions
§  Apache Felix SCR Tooling
§  Alternatives available J
§  Inter-operability through OSGi service registry
73

Conclusion
§  Today a lot of the hard work is already done
§  Open Source & Open Development are your friends
§  OSGi made the Adobe Experience Manager success story possible
§  Team growth from 40+ to several hundreds
§  Immense growth in functionality
§  Still (dynamically) extensible and manageable
§  OSGi Core and Compendium provide nearly everything you need
§  Framework, Declarative Services, Configuration Admin, Metatype, Event Admin
§  Open Source Implementations and Extensions
§  Apache Felix and friends
74

Check It Out!
•  Read the OSGi specs
•  Framework
•  Declarative Services, Config Admin, Metatype, Event Admin
•  Checkout the various Apache projects!
•  Explore available tooling
•  Embrace modularity!
•  Join the OSGi Alliance and help shaping the future!
75

And…New OSGi Specifications!
§  Last week (week of June 2nd) the OSGi Core Release 6 Specification received its final
approval and will be available this week to the public for downloading.
§  http://www.osgi.org/Specifications/HomePage
§  Also happening last week, the OSGi Board of Directors approved the publication of an
Early Draft Specification of OSGi Enterprise Release 6 for downloading.
§  http://www.osgi.org/Specifications/Drafts
76

References
§  OSGi Semantic Versioning Whitepaper: http://www.osgi.org/wiki/uploads/Links/SemanticVersioning.pdf
§  OSGi Specifications: http://www.osgi.org
§  Apache Felix: http://felix.apache.org
§  Apache Sling: http://sling.apache.org
§  Apache Aries: http://aries.apache.org
§  BND: http://www.aqute.biz/Bnd/Bnd
§  Bndtools: http://njbartlett.name/bndtools.html
§  Planet OSGi: http://www.osgi.org/Planet/Feed
77

Building Modular Enterprise Applications - C Ziegeler

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