I've recently done a couple projects writing D-Bus services. I've found them to be quite nice to use (once you get over the verbose connection strings). If you are on Linux, I'd suggest including D-Bus in your investigations.

These projects were in python, so I can't comment on Net::DBus specifically, but it looks to be the thing to use.

Some features: Is an RPC tool so using it is just calling methods, clients don't have to reconnect if your server process needs to restart, systemd integration means you can have your server process start on demand.

Update Upon looking at Rex, I'm not sure my suggestion is quite reasonable. I expected you were running something where you could split the slow start pieces into a service which exposes callable methods. Rex seems to be able to run in a server mode itself, so I don't see why you wouldn't use that -- I must be fundamentally misunderstanding what Rex does or what you want... Sorry