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Karaf provides a simple, yet flexible, way to provision applications or "features". Such a mechanism is mainly provided by a set of commands available in the features shell. The provisioning system uses xml "repositories" that define a set of features.

Repositories

The xml features repositories use the following Relax NG Compact syntax:

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A repository includes a list of feature elements, each one representing an application that can be installed. The feature is identified by its name which must be unique amongst all the repositories used and consists of a set of bundles that need to be installed along with some optional dependencies on other features and some optional configurations for the Configuration Admin OSGi service.

References to features define in other repositories are allow and can be achieved by adding a list of repository.

<features>
  <repository>mvn:org.apache.servicemix.nmr/apache-servicemix-nmr/1.2.0/xml/features</repository>
  <repository>mvn:org.apache.camel.karaf/apache-camel/2.2.0/xml/features</repository>
  <repository>mvn:org.apache.felix.karaf/apache-felix-karaf/1.4.0/xml/features</repository>
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Remark : By default, all the features defined in a repository are not installed at the launch of Apache Karaf (see section hereafter 'h2. Service configuration' for more info).

Bundles

The main information provided by a feature is the set of OSGi bundles that defines the application. Such bundles are URLs pointing to the actual bundle jars. For example, one would write the following definition:

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Repositories on the local are supported through file:/ URLs

Bundle start-level

By default, the bundles deployed through the feature mechanism will have a start-level equals to the value defined in the configuration file config.properties
with the variable karaf.startlevel.bundle=60. This value can be changed using the xml attribute start-level.

  <feature name='my-project' version='1.0.0'>
    <feature version='2.4.0'>camel-spring</feature>
    <bundle start-level='80'>mvn:com.mycompany.myproject/myproject-dao</bundle>    
    <bundle start-level='85'>mvn:com.mycompany.myproject/myproject-service</bundle>
    <bundle start-level='85'>mvn:com.mycompany.myproject/myproject-camel-routing</bundle>
  </feature> 

The advantage to define the start-level of a bundle is that you can deploy all your bundles including those of the project with the 'infrastructure' bundles required (e.g : camel, activemq)
at the same time and you will have the guaranty when you use Spring Dynamic Module (to register service through OSGI service layer), Blueprint that by example
Spring context will not be created without all the required services installed.

Dependant features

Dependant features are usefull when a given feature depends on another feature to be installed. Such a dependency can be expressed easily in the feature definition:

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A simple configuration file located in {{\[FELIX:karaf\]/etc/org.apache.servicemixkaraf.features.cfg}} can be modified to customize the behavior when starting the Kernel for the first time.
This configuration file contains two properties:

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This configuration file is of interest if you plan to distribute a ServiceMix Kernel Apache Karaf distribution which includes pre-installed features. Such a process is detailed in the 6.2. Building custom distributions section.

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