Assumptions

Each service assumes at the outset that it's the only one in existence.
Each service periodicially probes for the existence of other services.
If two services of the same type find one another, they'll link up and synchronize.
If three services of the same type exist, but A knows about B and B knows about A and C, B and C will synch, and then A and B will synch the content of B and C.

Problems

Service foo wants to search for services of the same type on other nodes that may or may not exist.
Service foo wants to use another piece of software running on the same node to search for other instances.
The datastore backing service foo isn't capable of synchronizing on its own with others of its type.
The datastore backing service foo cannot grow without bound.
Service foo isn't designed to have a web front end, but needs one.
- Service foo needs a plug-in that exposes the service over HTTP.
Each instance of service foo needs a unique identifier.

Designate a service on the node that maintains a catalogue of other services running on the node and make them available on the local network.
Designate a service on the node that listens for announcements of other services on neighboring nodes.
Designate a service on the node that watches for new instances of the same service to appear.
- The monitoring daemon checks to see if the service announcement has already been picked up.
- The monitoring daemon contacts the service's administrative interface and executes the necessary commands to inform it of a new instance to contact.
- Service foo contacts the new instance and initiates synchronization.

I guess I'm talking about ejabberd and avahi here. Maybe with some glue code and the odd exposed administrative interface.