Architecture 

The JMX Adapter Service manages the configuration and lifecycle of the MBean Server and provides access to it for applications, services, and libraries. A local MBean Server is created on each cluster element. The local MBean Servers communicate with each other, so that clients running inside the AS Java (Management Client B in the figure below) only have to interact with their local MBean Server. Each local MBean Server provides a virtual view of all MBeans in the cluster, that is, a client can access MBeans regardless of whether they are registered locally or on a remote cluster node.

The external clients (Management Client A in the figure below) must connect to the cluster using a JMX connector, based on the RMI-P4 protocol. The RMI-P4 call is dispatched to the server part of the JMX connector on an arbitrary server process, which in turn delegates the request to the local MBeanServer.

Interceptor Chain

 

The virtual MBean Server view is provided by an MBean Server interceptor, which redirects calls according to the location information in the ObjectName. The location information also guarantees unique ObjectNames across all cluster elements. There is a factory, which supports the creation of ObjectNames that include this location information. For local MBeans, the location information can be omitted, as in this case the ObjectName is automatically completed by another MBean Server interceptor. For more information, see com.sap.jmx.ObjectNameFactory.

Virtual MBean Server

The figure above illustrates which MBeans in the cluster are visible from the element on which the client currently resides. If the client resides on the cluster element with ID 4001, it will see all MBeans that are registered on the same element. It will also see those MBeans from remote nodes (in our case – Node 5001,) that include the element ID in their ObjectName.

MBeans that include a cluster element ID in their name are regarded as Local MBeans (the blue ones in the figure.) A local MBean represents an element-local aspect of a resource, that is, the state of the HTTP Provider Service on a single cluster element. The element ID in the ObjectName of an MBean is always equal to the ID of the cluster element where this MBean is registered. The element ID prevents not only name clashes, but is also used to address the proper MBean Server in the cluster. A special case of a local MBean is the MBean, which represents the cluster element itself.

The MBeans in the figure, colored yellow, are either Clustered MBeans – they represent a cluster-wide aspect of a resource – or Internal MBeans, which are only important for the cluster element they reside on. Both Internal and Clustered MBeans can only be accessed from the element they are registered with. The idea of the Clustered MBeans is that corresponding instances exist on each element in the cluster. Since all instances of a Clustered MBean represent the same aspect of the resource, there is no need to access an instance on a remote element. In the figure, FOO is a Clustered MBean.