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This discusses the various ways you can make Nimbus components behave differently, either by activating/switching pre-existing plugins or by creating a new plugin/component to replace a current extensibility point.
Each Nimbus component can be sanely replaced by something that implements the same interface or protocol.
This provides a wide range of possibilities. For example, this summer saw a drop-in workspace-control replacement that adds support for KVM virtual machines (this is a Google Summer of Code project whose result should be integrated into Nimbus officially in the future).
Also in many cases the pieces can be used on their own.
On top of all this, most of the Java based components have the built-in ability to define their internal modules at runtime via configuration files. This is achieved by using the Spring framework dependency injection container.
The workspace service has the most of these internal "plug points" (around 50, all told, although it would be esoteric to replace some of them).
The major ones are outlined on the following pages:
- Scheduling/resource management
- Networking leases
- Usage accounting
- Request authorization
- Initial request intake
- Fine grained replacement for VMM control tasks
A beginning exercise to start developing plugins would be to:
- Look at the Spring configuration for one of the current plugins in the list above.
- Find the source code for the implementation listed.
- Create your own new Java class based on that other implementation and change something around or print something new and prominent to the logger.
- Then put the fully qualified class name of your new class into the Spring configuration in place of the original class name.
- Make sure a jar file with your new compiled class exists under $GLOBUS_LOCATION/lib
- Reboot the container to see your change take effect.