This allows some uWSGI instances to announce their presence to subscriptions managing server,
which in its turn can address those nodes (e.g. delegate request processing to them)
and automatically remove dead nodes from the pool.
Some routers provide subscription server functionality. See .routing.routers.
Note
Subscription system in many ways relies on Master Process.
Warning
The subscription system is meant for "trusted" networks.
All of the nodes in your network can potentially make a total mess with it.