Welcome!

Microservices Expo Authors: Carmen Gonzalez, Yeshim Deniz, Liz McMillan, Elizabeth White, Reinhard Brandstädter

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
Join us at Cloud Expo | @ThingsExpo 2016 – June 7-9 at the Javits Center in New York City and November 1-3 at the Santa Clara Convention Center in Santa Clara, CA – and deliver your unique message in a way that is striking and unforgettable by taking advantage of SYS-CON's unmatched high-impact, result-driven event / media packages.
SYS-CON Events announced today that BMC Software has been named "Siver Sponsor" of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. BMC is a global leader in innovative software solutions that help businesses transform into digital enterprises for the ultimate competitive advantage. BMC Digital Enterprise Management is a set of innovative IT solutions designed to make digital business fast, seamless, and optimized from mainframe to mo...
SYS-CON Events announced today that Tintri Inc., a leading producer of VM-aware storage (VAS) for virtualization and cloud environments, will exhibit at the 18th International CloudExpo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, New York, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Isomorphic Software will exhibit at SYS-CON's [email protected] at Cloud Expo New York, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Isomorphic Software provides the SmartClient HTML5/AJAX platform, the most advanced technology for building rich, high-productivity enterprise web applications for any device. SmartClient couples the industry’s broadest, deepest UI component set with a java server framework to deliver an end-...
18th Cloud Expo, taking place June 7-9, 2016, at the Javits Center in New York City, NY, 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 enterprises are using some...
SYS-CON Events announced today the Docker Meets Kubernetes – Intro into the Kubernetes World, being held June 9, 2016, in conjunction with 18th Cloud Expo | @ThingsExpo, at the Javits Center in New York, NY. Register for 'Docker Meets Kubernetes Workshop' Here! This workshop led by Sebastian Scheele, co-founder of Loodse, introduces participants to Kubernetes (container orchestration). Through a combination of instructor-led presentations, demonstrations, and hands-on labs, participants learn ...
SoftLayer operates a global cloud infrastructure platform built for Internet scale. With a global footprint of data centers and network points of presence, SoftLayer provides infrastructure as a service to leading-edge customers ranging from Web startups to global enterprises. SoftLayer's modular architecture, full-featured API, and sophisticated automation provide unparalleled performance and control. Its flexible unified platform seamlessly spans physical and virtual devices linked via a world...
Just last week a senior Hybris consultant shared the story of a customer engagement on which he was working. This customer had problems, serious problems. We’re talking about response times far beyond the most liberal acceptable standard. They were unable to solve the issue in their eCommerce platform – specifically Hybris. Although the eCommerce project was delivered by a system integrator / implementation partner, the vendor still gets involved when things go really wrong. After all, the vendo...
SYS-CON Events announced today that AppNeta, the leader in performance insight for business-critical web applications, will exhibit and present at SYS-CON's @DevOpsSummit at Cloud Expo New York, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. AppNeta is the only application performance monitoring (APM) company to provide solutions for all applications – applications you develop internally, business-critical SaaS applications you use and the networks that deli...
SYS-CON Events announced today that EastBanc Technologies will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. EastBanc Technologies has been working at the frontier of technology since 1999. Today, the firm provides full-lifecycle software development delivering flexible technology solutions that seamlessly integrate with existing systems – whether on premise or cloud. EastBanc Technologies partners with p...
The initial debate is over: Any enterprise with a serious commitment to IT is migrating to the cloud. But things are not so simple. There is a complex mix of on-premises, colocated, and public-cloud deployments. In this power panel at 18th Cloud Expo, moderated by Conference Chair Roger Strukhoff, panelists will look at the present state of cloud from the C-level view, and how great companies and rock star executives can use cloud computing to meet their most ambitious and disruptive business ...
Many banks and financial institutions are experimenting with containers in development environments, but when will they move into production? Containers are seen as the key to achieving the ultimate in information technology flexibility and agility. Containers work on both public and private clouds, and make it easy to build and deploy applications. The challenge for regulated industries is the cost and complexity of container security compliance. VM security compliance is already challenging, ...
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
Agile teams report the lowest rate of measuring non-functional requirements. What does this mean for the evolution of quality in this era of Continuous Everything? To explore how the rise of SDLC acceleration trends such as Agile, DevOps, and Continuous Delivery are impacting software quality, Parasoft conducted a survey about measuring and monitoring non-functional requirements (NFRs). Here's a glimpse at what we discovered and what it means for the evolution of quality in this era of Continuo...
Last week I had the pleasure of speaking on a panel at Sapphire Ventures Next-Gen Tech Stack Forum in San Francisco. Obviously, I was excited to join the discussion, but as a participant the event crystallized not only where the larger software development market is relative to microservices, container technologies (like Docker), continuous integration and deployment; but also provided insight into where DevOps is heading in the coming years.
In the rush to compete in the digital age, a successful digital transformation is essential, but many organizations are setting themselves up for failure. There’s a common misconception that the process is just about technology, but it’s not. It’s about your business. It shouldn’t be treated as an isolated IT project; it should be driven by business needs with the committed involvement of a range of stakeholders.
You might already know them from theagileadmin.com, but let me introduce you to two of the leading minds in the Rugged DevOps movement: James Wickett and Ernest Mueller. Both James and Ernest are active leaders in the DevOps space, in addition to helping organize events such as DevOpsDays Austinand LASCON. Our conversation covered a lot of bases from the founding of Rugged DevOps to aligning organizational silos to lessons learned from W. Edwards Demings.
As AT&Ts VP of Domain 2.0 architecture writes one aspect of their Domain 2.0 strategy is a goal to embrace a Microservices Application Architecture. One page 9 they describe how these envisage them fitting into the ECOMP architecture: "The initial steps of the recipes include a homing and placement task using constraints specified in the requests. ‘Homing and Placement' are micro-services involving orchestration, inventory, and controllers responsible for infrastructure, network, and applicati...
Application development and delivery methods have undergone radical changes in recent years to improve scalability and resiliency. Container images are the new build and deployment artifacts that are used to ship and run software. While startups have long been comfortable experimenting with and embracing new technologies, even large enterprises are now re-architecting their software systems so that they can benefit from container-enabled micro services architectures. With the launch of DC/OS, w...
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...