Java Applications Replicating State

Question

I have the same server side application running on multiple machines.

I would like to provide a way to push changes to all the applications. I'm more interested in state/property changes to the objects themselves, and not so much replication of files, etc.

So I'm envisioning an admin console, where I would change some property, and have the change affect each applications state.

I am currently looking into JGroups, which is a toolkit for reliable multicast communication. In this case, each application would listen in on the same multicast group, and the admin console would send changes to the group.

Are there any other solutions/techniques available?

Answer 1

There exist alot of techniques, corba, rmi etc etc. However if you want a fully distributed system with no central server, I would personally recommend JGroups.

If you have a central server you can either

• Let the server push the changes to all clients. The server must be aware of all clients, either directly or by having the clients register themselves.
• Let clients poll the server.

Answer 2

Other simple solutions might including, polling a central database or a central file.

A quick Google search turns up: http://www.hazelcast.com/product.jsp. Which looks promising but I have no experience with it.

Answer 3

Apache ZooKeeper from the Hadoop project may also be interesting. I have no experience with it, but from the webpage I conlude it offers a hierarchical datamodel. Each application interested in changes can watch for changes in a specific node and act upon the changes.

http://zookeeper.apache.org/doc/trunk/index.html

Answer 4

For the more complex scenarios I can't recommend terracotta enough. Essentially terracotta distributes parts of your heap to the network, meaning that your applications share parts of the heap. Changes made by one app in the shared heap will be visible to the other applications sharing the heap. The main drawback is that terracotta needs a dedicated server since it's a hub and spoke design.