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Chapter 2. Writing Server-Side Plug-ins: Background
All JBoss ON plug-ins have a similar configuration and deployment style, with minor differences in what is required for the plug-ins to access the systems. Server-side plug-ins refer to any plug-in which accesses the core JBoss ON server to perform its actions; essentially, these are global plug-ins used for the central server behavior.
2.1. An Intro to Server-Side Plug-ins
Server-side plug-ins extend the functionality of the JBoss ON server. JBoss ON comes with several categories of server-side plug-ins already:
- Alert sender plug-ins for methods to send alert notifications for resources
- Bundle plug-ins for deploying files and application
- Drift plug-ins for monitoring resource or filesystem configuration and files
- Content plug-ins for managing resource configurations
- Generic plug-ins for everything else
Server-side plug-ins are not limited to those three categories; the server-side plug-in framework allows substantial access to the server itself. Server-side plug-ins can be used to run remote scripts in response to monitoring events or to provision systems in a custom work flow — anything that is within the purview of the JBoss ON server.
This is a much more casual approach to implementing plug-ins than the more structured, formal agent plug-in system. This allows much more latitude in what plug-in developers are able to accomplish.
IMPORTANT
All server-side plug-ins have full access to the server's stateless session beans (SLSBs). This allows a lot of latitude and versatility in the functionality of server-side plug-ins and allows access to any server subsystem. However, this also makes server-side plug-ins extremely powerful. Be cautious in writing and deploying server-side plug-ins.
Server-side plug-ins have a different framework for writing and deploying plug-ins than the framework for agent plug-ins. Here are some general bits of information that are useful as you begin writing server-side plug-ins:
- Once the server-side plug-in is built and deployed, the plug-in is a JAR file with a
META-INF/directory which contains therhq-serverplugin.xmlplug-in descriptor. - Each plug-in is independent of every other plug-in. Unlike agent plug-ins, server-side plug-ins do not interact with each other. There are no plug-in dependencies for server-side plug-ins.
Server-side plug-ins are organized according to their type, and the type corresponds to the subsystem or functional area which the plug-in extends. Each type of plug-in is contained within a defined plug-in container.
Server-side plug-ins are managed in the JBoss ON server within a plug-in container that relates to the function of the plug-in, and the plug-in container handles general tasks like starting and stopping plug-ins and providing general configuration settings for that type of plug-in. (All plug-in containers are, themselves, members of a single master plug-in container.)
Figure 2.1. Server-Side Plug-in Containers
There is only one plug-in container for each type of plug-in, but there can be an unlimited number of server-side plug-ins within each plug-in container.
NOTE
A plug-in container defines what type a plug-in is. A plug-in, then, can only be in one plug-in container because it can only be of one type.
Table 2.1, “Available Plug-in Containers” summarizes the available plug-in containers with JBoss ON.
Table 2.1. Available Plug-in Containers
| Plug-in Type | Description | Container Name |
|---|---|---|
| Generic | Catch-all type for any custom plug-ins. This type of plug-in only interacts with the plug-in container for the container to start and stop the plug-in and to initialize and shutdown the plug-in libraries. | Generic Plugin |
| Alert methods | Defines an alert notification method, or the way that an alert is sent. | AlertHandler |
| Bundle | Defines and processes a type of bundle. This type of plug-in performs tasks that the core server needs to process and manage bundles of specific bundle types, such as Ant recipes or file-based bundles. Each bundle server plug-in knows about and can process a single bundle type. | Bundle Plugin |
| Drift | Processes drift operations and configuration. This stores and retrieves content (files) being managed for drift detection and remediation. | Drift JPA Plugin |
| Content | Contains metadata for a a repository or a group of repositories. | PackageSource |
| Repository (also Package) | Defines a content repository. Plug-ins can define a single repository,which is then used for provisioning, entitlements, and updates for JBoss ON-managed resources. | ChannelSource |
NOTE
New plug-in containers cannot be created without rebuilding JBoss ON, because the plug-in containers are part of the core JBoss ON code. Rather than defining a new plug-in type, use the generic plug-in container, since this provides full access to the server functionality, anyway.
