I am very new to OSGi and Karaf and I am still getting my head around the concepts and architecture.
My question is related to the .kar files which are created with the karaf-maven-plugin.
Does a .kar file meant to only install features into a Karaf runtime? What if we create a bundle and rename it to .kar instead of .jar. Is this a valid use case for .kar files?
Thanks
No, a kar file is much more than that as it is a mechanism to provide not only the features.xml but also any related OSGi bundles, configuration files, aso. inside a single artifact.
That's also why it contains a mandatory repository/ directory (basically containing all OSGi bundles necessary for any of the features described by the features.xml in a Maven repository-style structure) and an optional resources/ directory (containing all the additional resources referenced by a feature).
For a fully fledged example, you can have a look at the Apache Karaf framework archive:
That one contains all the basic resources that make up the base for a custom Karaf installation and provide the basic set of features:
META-INF/
...
META-INF/MANIFEST.MF
...
repository/
... OSGi bundles referenced by the features and the features.xml itself ...
resources/
resources/bin/
... scripts ...
resources/data/
...
resources/deploy/
...
resources/etc/
... configuration files ...
resources/lib/
... (non-OSGi) libraries needed (e.g. endorsed, extension, boot classpath) ...
resources/system/
... OSGi framework implementation(s) and related libraries ...