OSGi Integration

Horizon uses the OSGi framework in a Karaf container. This section explains how to integrate a Maven module (OSGi bundle) in your Horizon instance.

Add Maven module

New Maven modules are usually distributed in the form of a bundle (a JAR file and OSGi metadata). After you create a Maven module, add this plugin to pom.xml to create the necessary metadata:


                    <!-- <Export-Package>org.foo.myproject.api</Export-Package>--> (1)
                    <!-- <Import-Package>org.foo.myproject.api.dependencies</Import-Package>--> (2)
                    <!-- <Private-Package>org.foo.myproject.impl</Private-Package>--> (3)
                    <!-- <Karaf-Commands>*</Karaf-Commands>--> (4)
1 (Optional) Define packages that can be exported.
2 (Optional) Define packages to import from dependent modules.
3 (Optional) Define private packages that should not be exported.
4 Include this only when the module is intended for adding Karaf commands.

Add Karaf feature

A feature is a set of bundles that can be installed in Karaf. For any given module, all of its dependencies must be specified in a feature. Sometimes, there are runtime dependencies that will run only when you actually use the feature.

Example feature definition
   <feature name="scv-api" version="${project.version}" description="Secure Credentials Vault">
    <feature name="scv-jceks-impl" version="${project.version}" description="Secure Credentials Vault JCEKS Impl">
        <bundle dependency="true">mvn:commons-codec/commons-codec/${commonsCodecVersion}</bundle>
        <bundle dependency="true">mvn:com.google.guava/guava/${guavaVersion}</bundle>

You can define features by editing the files located in container/features/src/main/resources/:

  • features.xml: All features specific to Horizon and those common to Minion and Sentinel.

  • features-minion.xml: All features specific to Minion.

  • features-sentinel.xml: All features specific to Sentinel.

To make a feature available in the Karaf container, add the feature and any appropriate dependencies to the following files:

  • Horizon: opennms-full-assembly/pom.xml

  • Minion: features/minion/repository/pom.xml (feature and Maven dependencies)

  • Sentinel: features/sentinel/repository/pom.xml (feature and Maven dependencies)

Install feature by default

To install a new feature by default, edit the following files:

  • Horizon: Add the feature in container/karaf/src/main/filtered-resources/etc/org.apache.karaf.features.cfg.

  • Minion: Add the feature in features/minion/repository/src/main/resources/features.boot.

  • Sentinel: Add the feature in features/container/sentinel/src/main/filtered-resources/etc/org.apache.karaf.features.cfg.

Spring Maven modules

If a Maven module should be loaded in Spring by default, you must include it in opennms-base-assembly/pom.xml. All of the modules that are loaded in Spring will be made available in ${opennms.target}/opennms/lib.

Some modules are defined only in Spring (legacy RPC modules, such as opennms-services). These are loaded in the default classloader.

You can add Spring beans to the OSGi service registry by exposing the beans as <onmsgi:service>.

Add package to custom.properties

Packages added to custom.properties are loaded in the default classloader, even when loaded in OSGi. You must use custom.properties to export packages that are loaded in Spring, but are also accessed through OSGi.

Health check

The health check command is available in all Karaf containers:


It validates whether all features are enabled and running without issue in your Horizon environment. If you see any bundle-related failures, you can use bundle:diag id to retrieve more specific information.

Dynamically reload module for debugging

You can use the bundle:watch * command to dynamically reload a module. This lets you watch the module for behaviors that may be of interest during the debugging process.

You can also use bundle:watch~ in the Karaf container to watch for any updates in the local m2 repository.

To update a specific module in your local Karaf repository, use mvn clean install in the appropriate directory.

Disable Karaf SSH host key check

To disable the host key check function for SSH in your Karaf container, add the following code to .ssh/config:

Host localhost
    HostKeyAlgorithms +ssh-dss
    StrictHostKeyChecking no