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The Kernel

The Fuse ESB kernel is based on Apache Karaf, an OSGi-based runtime that provides a lightweight container into which you can deploy various components and applications.

The kernel provides the following features:

OSGi is set of open specifications aimed at making it easier to build and deploy complex software applications. The key piece of OSGi technology is the OSGi Framework. The framework manages the loading and management of dynamic modules of functionality.

In an OSGi environment applications are packaged into bundles. A bundle is a JAR that contains extra information about the classes and resources included in the bundle. The information supplied in the bundle includes:

  • packages required by classes in the bundle

  • packages being exported by the bundle

  • version information for the bundle

Using the information in the bundle, the OSGi framework ensures that all of the dependencies required by the bundle are present. If it is, the bundle is activated and made available. The information in the bundle also allows the framework to manage multiple versions of a bundle.

The OSGi specifications are maintained by the OSGi Alliance. See

For more information about Fuse ESB's OSGi functionality see Deploying into the OSGi Container.

OSGi offers a number of benefits over other container and packaging models including:

Karaf supports the following OSGi 4.2 containers:

  • Apache Felix Framework 2.0.0

  • Eclipse Equinox 3.5.

In Fuse ESB 4.3.1, the default container is Equinox. To change your OSGi container, set the karaf.framework property to felix in the etc/ file.