Just heads up, people should know libp2p (unless something has changed?) still has flooding problems. There are other P2P transport alternatives, check out SSB's (it is really good!) or ours (gun.eco/docs/DAM) which prevents flooding. WebRTC and websocket implementations exist.
In any case, floodsub is just one option you can use for pubsub on top of libp2p (one with a notably high level of reliability and minimal cross network latency for infrequent messaging). We also have a tree pruning gossiping implementation called gossipsub. Take a look at the spec: https://github.com/libp2p/specs/blob/master/pubsub/gossipsub...