More generically, since there are hubzilla hubs and other things, how does a new “node” (i.e. pod, hub, etc) discover existing nodes? Similarly, how do existing nodes become aware of a new node?
From what I can find, it seems like it’s done by a person running a search using a known user ID (e.g. email@example.com).
In Diaspora pods are initially not aware of other pods. All interactions are sent to specific users.
However when an user adds someone to their aspects they start sending their posts to that person and get public posts from them. So these public posts become available for everyone else on their pods. When pod has many users each having added contacts from all over the network the pod gets a lot of interactions and public stream full of activity.
Another mechanism of getting new content is social relay. If pod admin chooses so they may connect their pod to relay server which forwards all public posts to/from them to other pods to increase coverage. This is mostly relevant for small/personal pods which might be not well connected otherwise.