A simple Beatrix application

Here's how we use Beatrix to write and use a simple distributed application which will serve a hello world message to a console. The principles of plugins have been covered in Chapter  but see Chapter  for the deeper details of all this code.

The application will:

• Provide an administation service through the managers, allowing the application owner to control it. This service will be called admin.
• Provide a consumer service through workers, allowing them to serve the hello world message to any console that connects to them. This service will be called skeleton.
• Maintain redundancy by keeping 2-4 managers alive at all times.
• Maintain redundancy by keeping 2-4 workers alive at all times.
• Demand network and disk resources for workers (though it doesn't use either).
• Have managers adding plugins to new workers remotely.

Additionally Beatrix does the following for us:

• Maintains redundancy by ensuring each worker runs on a different node.
• Maintains redundancy by ensuring each manager runs on a different node.
• Allows unused resources to be released or re-used as necessary.
• Allows launch and management through a command line console.

We need to implement five plugins and one interface--see Figure  for a visual overview. The interface:

• ISkeletonFacet. An interface that contains the getMessage() method, providing the hello world message.

The plugins:

• AdminServiceProvider. Provides the owner's administration service. We will call the service admin.
• SkeletonServiceProvider. Provides the basic consumer service to deliver the hello world message. We call this service skeleton.
• LifeCyclePlugin. Handles the managers' life cycles: cold starts, warm starts, joining and leadership changes. Program flow starts here.
• SkeletonWorkerManager. A plugin to the managers which sets up the workers. Sets their resource requirements and remotely adds the plugins they need.
• SkeletonWorker. The main worker plugin. It binds the resources allocated to it but doesn't use them.

An additional class, SkeletonFacet, is included in the SkeletonWorker.java file. It implements the ISkeletonFacet.