• Compass is used as a search engine by a few dozen / hundreds Web Front ends.
• Any of these web front ends might, once in a while, want to update compass index, and broadcast the changes so that others can work on up to date data
• A new web front end might show up, and ask for the whole compass index to create its initial search index

To make things fully automatic, something like ActiveCluster (http://activecluster.codehaus.org/) could be used to discover new parties interested in joining the cluster.

Concrete Use Case :

• dozens of web front ends use Compass to query a database of cities
• once in a while, a city is added by a user on any of the servers
• this server updates its index, and propagates the changes to all other servers.

Regards,
Sami Dalouche