JMX Notifications Support

There are 3 ways how the notifications could be supported:

• Client Pull The agent itself registers for certain notifcation on behalf of a client and queues the notifications arriving. The client then needs to query the agent itself for getting arrived notification, either directly by a request with a new type or the new notifications are added piggy pack to the respone of any request. The advantage of this solution is, that the communication direction and initiation is the same as for all other request, so no extra constraints related to the network topology are required.

• Active Server Push by using HTTP In this scenario, the agent on the server side contacts an URL actively when a notification arrives. This URL has been provided by the client when it registers for a notification. Advantage of this solution is that there are no extra requirements for the server where the agent is deployed and that this is a real push as well. However, the flow of communication is reversed, i.e. the agent needs to initiate and issue an HTTP request, which can get quite problematic for certain firewall setups. Also, the result of the push needs to be evaluated on a server as well, so this is not something which will work with every client (e.g. the Javascript client running in a Browser. Of course, WebSockets could be an option here as well).

• Server Push via Ajax Push The client and agent uses a hanging GET for direct server push notification. This is the 'classic' HTTP solution for server push, but has certain requirements on the server side, which probably are not always given for any environment. I'm no expert in the Comet model, so I don't know in detail how the server needs to be prepared. Advantage would be, that this is a real push and the network flow is still from client to server.

Jolokia could support one, two or all of the possibilities.