Welcome!

Microservices Expo Authors: Elizabeth White, Liz McMillan, Ruxit Blog, Daniel Khan, Sematext Blog

Related Topics: Microservices Expo, Java IoT, Industrial IoT, IoT User Interface

Microservices Expo: Article

The OSGi puzzle

Let's discover the OSGi architecture.

OSGi became very popular thanks to its modularity approach and its ability to enforce logical boundaries between modules. When we discover it the first time, the question is where to begin to understand how it works?

To understand OSGi concepts we will try to follow the puzzle approach. The idea is to begin with the trivial part of this technology, and search for other parts related to the found ones. And to assemble the puzzle we will be assisted by JArchitect that will be helpful to detect OSGi internal design.

To be more concrete we analyze with JArchitect an application using OSGi technology, it concern the famous eclipse IDE which use the OSGi container equinox.



Let's begin with the typical OSGi definition:

OSGi reduces complexity by providing a modular architecture for today's large-scale distributed systems as well as small, embedded applications. Building systems from in-house and off-the-shelf modules significantly reduces complexity and thus development and maintenance expenses. The OSGi programming model realizes the promise of component-based systems.

The trivial part of OSGi is modularity, let's discover what's the OSGi modules

OSGI modules are called Bundles and every application therefore consist of at least one bundle.

These bundles are executed inside a container, and as each modular approach where a container manage the modules, the question is which contract must implement every module to be intergated into the container?

Let's take as example the bundle org.eclipse.equinox.jsp.jasper and search for all its implemented interfaces, for that we can execute the following CQLinq request:

from t in Types where t.ParentProject.Name=="org.eclipse.equinox.jsp.jasper_1.0.300.v20110502" let interfaces=t.InterfacesImplemented from i in interfaces select i



The BundleActivator interface from OSGi package is implemented, this interface contains two methods start and stop useful to customizes the starting and stopping of the bundle.

Manifest-Version: 1.0

Bundle-Localization: plugin

Bundle-RequiredExecutionEnvironment: CDC-1.0/Foundation-1.0,J2SE-1.3

Bundle-SymbolicName: org.eclipse.equinox.jsp.jasper

Eclipse-LazyStart: true

Eclipse-SourceReferences: scm:cvs:pserver:dev.eclipse.org:/cvsroot/rt:

 org.eclipse.equinox/server-side/bundles/org.eclipse.equinox.jsp.jaspe

 r;tag=v20110502

Bundle-Activator: org.eclipse.equinox.internal.jsp.jasper.Activator


Another specificity of a bundle is its manifest file, here's a part from the org.eclipse.equinox.jsp.jasper manifest file:

Manifest-Version: 1.0

Bundle-Localization: plugin

Bundle-RequiredExecutionEnvironment: CDC-1.0/Foundation-1.0,J2SE-1.3

Bundle-SymbolicName: org.eclipse.equinox.jsp.jasper

Eclipse-LazyStart: true

Eclipse-SourceReferences: scm:cvs:pserver:dev.eclipse.org:/cvsroot/rt:

 org.eclipse.equinox/server-side/bundles/org.eclipse.equinox.jsp.jaspe

 r;tag=v20110502

Bundle-Activator: org.eclipse.equinox.internal.jsp.jasper.Activator

As we can observe this manifest contains some meta informations needed by the container, like specifying the bundle activator class which implements the BundleActivator interface.

The bundle represent our first piece of the puzzle,and here's a simplified representation of a bundle:



And just to have an idea of all bundles used by eclipse, let's search for all classes implementing BundleActivator interface.

from t in Types where t.Implement ("org.osgi.framework.BundleActivator") select new { t, t.NbBCInstructions }



Who manage the bundle and invoke BundleActivator methods?

To discover that let's search for methods invoking directly or indirectly BundleActivator.start

from m in Methods let depth0 = m.DepthOfIsUsing ("org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleActivator)") where depth0 >= 0 orderby depth0 select new { m, depth0 }



The bundle is activated by the OSGi framework when it's launched. the framework class is started by the equinox container. And to understand better what happen when the container start, here are some actions executed when the container is launched:



When the container is launched, it initialize the OSGi framework, the framework gets all installed bundles, and for each one it create an instance of BundleHost class, and store into a repository the found bundle.

The BundleHost class implement the Bundle interface, which contains methods like start,stop,uninstall and update, these methods are needed to manage the bundle life cycle.

So our second puzzle piece is The OSGi container, it's launched by the Equinoxlauncher, which initialise the framework. The framework class is responsible of loading bundles and activate them.

After discovering some basic concepts about bundle and container, let's go deep inside bundles and discover how they works internally.

Let's take as example the org.eclipse.equinox.http.servlet bundle and search for methods invoked by the start method of its Activator class.



This bundle create a service and register it into the container. A service in OSGi is defined by a standard Java class or interface. Typically a Java interface is used to define the service interface. The service is the preferred method bundles should use to communicate between each other.

Here are some useful scenarios of using services:

  • Export functionality from a bundle to other bundles.
  • Import functionality from other bundles.
  • Register listeners for events from other bundles.


Another remark from the previous dependecy graph is that a service factory is used to create the service instance.

Our third piece of the puzzle is the OSGi services layer, each bundle can use or declare some services , what enforce the component design approach, here's the new representation of the OSGi bundle.



If The bundle use services to communicate with other bundles, how it communicate with other jars?

If we develop a bundle and try to use a class from another jar, we can be surprised that it will not works as expected, the reason is that the ClassLoader is hooked by the OSGi container, to check that let's search which method invoke java.lang.Thread.setContextClassLoader.

from m in Methods where m.IsUsing ("java.lang.Thread.setContextClassLoader(ClassLoader)") select new { m, m.NbBCInstructions }



Many methods invoke it including the EquinoxLauncher. so every time the bundle try to create a class instance, the OSGi container will check if the code is permited to did this action or not, and here come the role of imported and exported package in the manifest file.

Export-Package: org.eclipse.equinox.http.servlet;version="1.1.0"



Import-Package: javax.servlet;version="2.3",javax.servlet.http;version

 ="2.3",org.osgi.framework;version="1.3.0",org.osgi.service.http;versi

 on="[1.2,1.3)" 



The bundle declare explicitly exported and imported package, and to check that , let's search for packages used by org.eclipse.equinox.http.servlet bundle and verify if it use only package imported.

from n in Packages where n.IsUsedBy ("org.eclipse.equinox.http.servlet_1.1.200.v20110502") select new { n, n.NbBCInstructions }



As we can observe all packages used are specified in the manifest file , in the import package section.
The exported package however represent the package that can be used from other bundles. it's represented by the ExportedPackage interface, and we can search for the container classes using this interface.

from t in Types where t.IsUsing ("org.osgi.service.packageadmin.ExportedPackage") select new { t, t.NbBCInstructions }



What interesting with this new capability, is that the bundle will have a well defined boundary, and what it use and what it expose as services is very well specified.

We can enforce the check of using imported packages by using other tools, for example with CQLinq we can write some rules warning each time a project use packages other than specified ones, but it's better to have this check in the execution environement, so the developer can't break this rules.

This capability to treat imported and exported packages is managed by the OSGi modules layer and it was our fourth piece of the puzzle.

Let's come back to the OSGi container and discover which services it provides?

Container services

As we discoverd before the container is launched by the EquinoxLauncher class and the framework class initialise and launch the bundles, to detect which services re provided let's search for all classes used in the framework initalisation method.
from t in Types where t.IsUsedBy ("org.eclipse.osgi.framework.internal.core.Framework.initialize(FrameworkAdaptor)") select new { t, t.NbBCInstructions }

Some classes are already discovered before like BundleRepository,BundleHost,PackageAdminImpl and ServiceRegistry.

What about the other classes:

  • StartLevelManager: Each OSGi Bundle is associated with a start level that enable the server to control the relative starting and stopping order of bundles. Only bundles that have a start level less or equal to the active start level of the server framework must be active. Usually, a bundle with a smaller start level tend to be started earlier.
  • SecurityAdmin: The security layer handles the security aspects by limiting bundle functionality to pre-defined capabilities.
  • EventManager: The Event Admin service provides a publish-subscribe model for handling events. It is realized according to the OSGi Event Admin Service Specification. The Event Admin service dispatches events between Event Publishers and Event Subscribers (Event Handlers) by interposing an event channel. Publishers post events to the channel and the event channel defines which handlers needs to be notified. Thus publishers and handlers have no direct knowledge of each other, which simplifies event management.


The OSGi whole picture
Let's assemble all puzzle pieces described before , and we will have the following OSGi picture:


This architecture has the following interesting benefits:

  • Simple.
  • Reduced Complexity.
  • Easy Deployment.
  • Secure.


What makes it very attractif and Worth a Detour, and you will not waste your time if you study it in depth.

More Stories By Lahlali Issam

Lahlali Issam Lead Developer at JavaDepend, a tool to manage and understand complex Java code. With JavaDepend, software quality can be measured using Code Metrics, visualized using Graphs and Treemaps, and queried using CQL language, a SQL like to query the code base.

@MicroservicesExpo Stories
SYS-CON Events announced today that Isomorphic Software will exhibit at DevOps Summit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Isomorphic Software provides the SmartClient HTML5/AJAX platform, the most advanced technology for building rich, cutting-edge enterprise web applications for desktop and mobile. SmartClient combines the productivity and performance of traditional desktop software with the simp...
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
This digest provides an overview of good resources that are well worth reading. We’ll be updating this page as new content becomes available, so I suggest you bookmark it. Also, expect more digests to come on different topics that make all of our IT-hearts go boom!
This complete kit provides a proven process and customizable documents that will help you evaluate rapid application delivery platforms and select the ideal partner for building mobile and web apps for your organization.
Node.js and io.js are increasingly being used to run JavaScript on the server side for many types of applications, such as websites, real-time messaging and controllers for small devices with limited resources. For DevOps it is crucial to monitor the whole application stack and Node.js is rapidly becoming an important part of the stack in many organizations. Sematext has historically had a strong support for monitoring big data applications such as Elastic (aka Elasticsearch), Cassandra, Solr, S...
It's been a busy time for tech's ongoing infatuation with containers. Amazon just announced EC2 Container Registry to simply container management. The new Azure container service taps into Microsoft's partnership with Docker and Mesosphere. You know when there's a standard for containers on the table there's money on the table, too. Everyone is talking containers because they reduce a ton of development-related challenges and make it much easier to move across production and testing environm...
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
Deploying applications in hybrid cloud environments is hard work. Your team spends most of the time maintaining your infrastructure, configuring dev/test and production environments, and deploying applications across environments – which can be both time consuming and error prone. But what if you could automate provisioning and deployment to deliver error free environments faster? What could you do with your free time?
Monitoring of Docker environments is challenging. Why? Because each container typically runs a single process, has its own environment, utilizes virtual networks, or has various methods of managing storage. Traditional monitoring solutions take metrics from each server and applications they run. These servers and applications running on them are typically very static, with very long uptimes. Docker deployments are different: a set of containers may run many applications, all sharing the resource...
SYS-CON Events announced today that 910Telecom will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
SYS-CON Events announced today that eCube Systems, a leading provider of middleware modernization, integration, and management solutions, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. eCube Systems offers a family of middleware evolution products and services that maximize return on technology investment by leveraging existing technical equity to meet evolving business needs. ...
The following fictional case study is a composite of actual horror stories I’ve heard over the years. Unfortunately, this scenario often occurs when in-house integration teams take on the complexities of DevOps and ALM integration with an enterprise service bus (ESB) or custom integration. It is written from the perspective of an enterprise architect tasked with leading an organization’s effort to adopt Agile to become more competitive. The company has turned to Scaled Agile Framework (SAFe) as ...

Modern organizations face great challenges as they embrace innovation and integrate new tools and services. They begin to mature and move away from the complacency of maintaining traditional technologies and systems that only solve individual, siloed problems and work “well enough.” In order to build...

The post Gearing up for Digital Transformation appeared first on Aug. 28, 2016 03:15 PM EDT  Reads: 1,618

DevOps at Cloud Expo – being held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Am...
Thomas Bitman of Gartner wrote a blog post last year about why OpenStack projects fail. In that article, he outlined three particular metrics which together cause 60% of OpenStack projects to fall short of expectations: Wrong people (31% of failures): a successful cloud needs commitment both from the operations team as well as from "anchor" tenants. Wrong processes (19% of failures): a successful cloud automates across silos in the software development lifecycle, not just within silos.
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
Cloud Expo 2016 New York at the Javits Center New York was characterized by increased attendance and a new focus on operations. These were both encouraging signs for all involved in Cloud Computing and all that it touches. As Conference Chair, I work with the Cloud Expo team to structure three keynotes, numerous general sessions, and more than 150 breakout sessions along 10 tracks. Our job is to balance the state of enterprise IT today with the trends that will be commonplace tomorrow. Mobile...
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long dev...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...