Welcome!

Microservices Expo Authors: Jyoti Bansal, Gordon Haff, Elizabeth White, Gopala Krishna Behara, Sridhar Chalasani

Related Topics: Microservices Expo, Java IoT, Industrial IoT, Machine Learning

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
The rise of containers and microservices has skyrocketed the rate at which new applications are moved into production environments today. While developers have been deploying containers to speed up the development processes for some time, there still remain challenges with running microservices efficiently. Most existing IT monitoring tools don’t actually maintain visibility into the containers that make up microservices. As those container applications move into production, some IT operations t...
We call it DevOps but much of the time there’s a lot more discussion about the needs and concerns of developers than there is about other groups. There’s a focus on improved and less isolated developer workflows. There are many discussions around collaboration, continuous integration and delivery, issue tracking, source code control, code review, IDEs, and xPaaS – and all the tools that enable those things. Changes in developer practices may come up – such as developers taking ownership of code ...
For organizations that have amassed large sums of software complexity, taking a microservices approach is the first step toward DevOps and continuous improvement / development. Integrating system-level analysis with microservices makes it easier to change and add functionality to applications at any time without the increase of risk. Before you start big transformation projects or a cloud migration, make sure these changes won’t take down your entire organization.
As Enterprise business moves from Monoliths to Microservices, adoption and successful implementations of Microservices become more evident. The goal of Microservices is to improve software delivery speed and increase system safety as scale increases. Documenting hurdles and problems for the use of Microservices will help consultants, architects and specialists to avoid repeating the same mistakes and learn how and when to use (or not use) Microservices at the enterprise level. The circumstance w...
SYS-CON Events announced today that Catchpoint Systems, Inc., a provider of innovative web and infrastructure monitoring solutions, has been named “Silver Sponsor” of SYS-CON's DevOps Summit at 18th Cloud Expo New York, which will take place June 7-9, 2016, at the Javits Center in New York City, NY. Catchpoint is a leading Digital Performance Analytics company that provides unparalleled insight into customer-critical services to help consistently deliver an amazing customer experience. Designed ...
@DevOpsSummit at Cloud taking place June 6-8, 2017, at Javits Center, New York City, is co-located with the 20th International 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 developm...
SYS-CON Events announced today that Outlyer, a monitoring service for DevOps and operations teams, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Outlyer is a monitoring service for DevOps and Operations teams running Cloud, SaaS, Microservices and IoT deployments. Designed for today's dynamic environments that need beyond cloud-scale monitoring, we make monitoring effortless so you...
Cloud Expo, Inc. has announced today that Andi Mann and Aruna Ravichandran have been named Co-Chairs of @DevOpsSummit at Cloud Expo 2017. The @DevOpsSummit at Cloud Expo New York will take place on June 6-8, 2017, at the Javits Center in New York City, New York, and @DevOpsSummit at Cloud Expo Silicon Valley will take place Oct. 31-Nov. 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that CA Technologies has been named “Platinum Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business – from apparel to energy – is being rewritten by software. From ...
DevOps and microservices are permeating software engineering teams broadly, whether these teams are in pure software shops but happen to run a business, such Uber and Airbnb, or in companies that rely heavily on software to run more traditional business, such as financial firms or high-end manufacturers. Microservices and DevOps have created software development and therefore business speed and agility benefits, but they have also created problems; specifically, they have created software securi...
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 with...
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm. In his general session at 20th Cloud Expo, Chris Brown, a Solutions Marketing Manager at Nutanix, will explore...
This week's news brings us further reminders that if you're betting on cloud, you're headed in the right direction. The cloud is growing seven times faster than the rest of IT, according to IDC, with a 25% spending increase just from 2016 to 2017. SaaS still leads the pack, with an estimated two-thirds of public cloud spending going that way. Large enterprises, with more than 1,000 employees, are predicted to account for more than half of cloud spending and have the fastest annual growth rate.
All clouds are not equal. To succeed in a DevOps context, organizations should plan to develop/deploy apps across a choice of on-premise and public clouds simultaneously depending on the business needs. This is where the concept of the Lean Cloud comes in - resting on the idea that you often need to relocate your app modules over their life cycles for both innovation and operational efficiency in the cloud. In his session at @DevOpsSummit at19th Cloud Expo, Valentin (Val) Bercovici, CTO of Soli...
Microservices are a very exciting architectural approach that many organizations are looking to as a way to accelerate innovation. Microservices promise to allow teams to move away from monolithic "ball of mud" systems, but the reality is that, in the vast majority of organizations, different projects and technologies will continue to be developed at different speeds. How to handle the dependencies between these disparate systems with different iteration cycles? Consider the "canoncial problem" ...
After more than five years of DevOps, definitions are evolving, boundaries are expanding, ‘unicorns’ are no longer rare, enterprises are on board, and pundits are moving on. Can we now look at an evolution of DevOps? Should we? Is the foundation of DevOps ‘done’, or is there still too much left to do? What is mature, and what is still missing? What does the next 5 years of DevOps look like? In this Power Panel at DevOps Summit, moderated by DevOps Summit Conference Chair Andi Mann, panelists l...
When building DevOps or continuous delivery practices you can learn a great deal from others. What choices did they make, what practices did they put in place, and how did they connect the dots? At Sonatype, we pulled together a set of 21 reference architectures for folks building continuous delivery and DevOps practices using Docker. Why? After 3,000 DevOps professionals attended our webinar on "Continuous Integration using Docker" discussing just one reference architecture example, we recogn...
Hardware virtualization and cloud computing allowed us to increase resource utilization and increase our flexibility to respond to business demand. Docker Containers are the next quantum leap - Are they?! Databases always represented an additional set of challenges unique to running workloads requiring a maximum of I/O, network, CPU resources combined with data locality.
Thanks to Docker and the DevOps revolution, microservices have emerged as the new way to build and deploy applications — and there are plenty of great reasons to embrace the microservices trend. If you are going to adopt microservices, you also have to understand that microservice architectures have many moving parts. When it comes to incident management, this presents an important difference between microservices and monolithic architectures. More moving parts mean more complexity to monitor an...
In recent years, containers have taken the world by storm. Companies of all sizes and industries have realized the massive benefits of containers, such as unprecedented mobility, higher hardware utilization, and increased flexibility and agility; however, many containers today are non-persistent. Containers without persistence miss out on many benefits, and in many cases simply pass the responsibility of persistence onto other infrastructure, adding additional complexity.