Introducing the No-op plugin for RHQ

“A no-op plugin, does that make sense?” you will ask - and indeed it makes sense when you look at recent developments inside RHQ with the REST-api and also the support for jar-less plugins.

The no-op plugin is meant to support jar-less plugins that are written to define ResourceTypes on the server along with their metrics in order to be usable via the REST api, but where no resources are supposed to be found via the classic java-agent.

A concrete use case is the work our GSoC student Krzysztof is doing by bridging monitoring data from CIMmons deployed e.g. in RHEL servers to RHQ resources. Here we have the (possible) need to define resource types that will only be fed via the REST api.

How do I use this?

Basically you write a plugin descriptor (either in the classical way which you then put into a plugin jar) or with the name of *-rhq-plugin.xml and then deploy that into the server. The contents of this descriptor then refer to the No-op plugin - first in the <plugin> elements’s package declaration:

<plugin name="bar-test"
    version="4.5.1"
    displayName="Jar less plugin test"
    description="Just testing"
    package="org.rhq.plugins.noop”
    xmlns="urn:xmlns:rhq-plugin"
    xmlns:c="urn:xmlns:rhq-configuration">

The next part is then to declare a dependency on the No-op plugin to be able to use the classes:

   <depends plugin="No-op" useClasses="true"/>

And finally to use the NoopComponent for the discovery and component classes of <server>s and <service>s:

    <server name="test"
        discovery="NoopComponent"
        class="NoopComponent"
        >
     …
    </server>
</plugin>

A plugin defined like this then defines metrics etc. just like every other plugin. This is the plugin info:

And the metric definition templates: