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This subsystem continues to use the OSGi mechanism to persistently track configurable parameters in the local instance context and to notify components when the parameters change. In this way the application components can continue to use the standard and well-understood OSGi configuration via ComponentContext. Furthermore, if components use the Apache Felix compile-time @Parameter @Property annotation, ONOS build process generates a configuration catalog as a jar/bundle resource, which the component can register, allowing the ONOS administrator to see what parameters can be configured. The component configuration subsystem will then make sure that when a change is made on one ONOS instance, the same change will be propagated across the entire ONOS cluster and reflected on all ONOS instances in that cluster.

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To allow parameters to be configurable, components must first designate their fields using the @ParameterProperty annotation as follows:

private static final int DEFAULT_MAX_EVENTS = 1000;

@Property(name = "maxEvents", intValue = DEFAULT_MAX_EVENTS,
        label = "Maximum number of events to accumulate")
private int maxEvents = DEFAULT_MAX_EVENTS;

private static final int DEFAULT_EMAIL = "onos-dev@onosproject.org";

@Property(name = "notificationEmail", value = DEFAULT_EMAIL,
          label = "Notification email address")
private String notificationEmail = DEFAULT_EMAIL;

In order to allow these parameters to be changed dynamically, a component should define a modified method, annotated using @Modify@Modified compile-time annotation as in this example:

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