11. An article of manufacture, comprising: a machine readable storage medium comprising instructions, that when executed by a processor, cause the processor to: execute a plurality of work processes in application server instances in a cluster of application server instances; establish internal connections for internal cluster communication between a message server and each of the plurality of work processes executing in the application server instances, wherein internal cluster communication comprises internal communications relating to at least one of events occurring in the cluster and an exchange of messages between work processes executing in the application server instances, the internal connections separate from connections for external cluster communication; provide a message service for the internal cluster communication, the internal cluster communication including inter-application server instance communication via the message server in accordance with a connection-based message passing protocol in which an internal connection established in the message server receives a notification message for each event occurring in the cluster and sends acknowledgement messages to internal connections established in the application server instances responsive to receiving messages being exchanged between work processes executing in the application server instances, the message server being shared by the application server instances through the established internal connections for internal cluster communication between the message server and each of the plurality of work processes executing in the application server instances; manage internal cluster communication in accordance with the connection-based message passing protocol, the internal cluster communication sent over the established internal connections for internal cluster communication between the message server and each of the plurality of work processes executing in the application server instances, including causing the processor to: communicate an event from an application server instance in the cluster of application server instances to the message server, including sending a notification message of the event to the message server; relay the notification message of the event in the cluster from the message server to one or more of the application server instances and cause a function to be performed in the one or more of the application server instances responsive to receiving the relayed notification message; and communicate messages being exchanged between the work processes executing in the application server instances in the cluster via the message server, including: acknowledge receipt of messages received from the work processes; and relay messages received from an originating work process to a destination work process, including replicating a multicast message received from the originating work process for broadcast to all other work processes executing in the application server instances.
20. The article of manufacture of claim 11 , wherein messages to be exchanged between work processes executing in the application server instances include messages to update state information in the cluster, the state information in the cluster comprising: adding a work process; removing the work process; changing a state of the work process; and changing an availability of a work process to communicate with other work processes in the cluster.