Gossipsub with relays

I have non-public nodes A and B connected to a public relay node, with kademlia, identify, dcutr, autonat and gossipsub behaviours (relay node using relay instead of dcutr).

Nodes A and B are subscribed to the same topic. Messages broadcasted to the topic by A result in an InsufficientPeers error and B does not receive the message. Is this expected, if so is there a way around this?

I’m imagining a system with many web / non-public nodes that will rely on public relays but each constantly subscribing to new topics and broadcasting messages frequently.

If this use case is feasible, what is the most idiomatic method to discover public relays, would it be using rendezvous?

Any insight would be appreciated, thanks!

After finding some new sources on the topic I believe I have a solid understanding of this now but will still leave this post open for anyone else interested in the future:

I’ve realized that nodes will only propagate a message if it is subscribed to the topic of the message. This concerned me that a message from node A won’t reach node B if each of the node A’s direct peers aren’t subscribed, which is true. But by nature of gossipsub with kademlia, nodes should gossip around subscriptions and form connections with other peers on the network also subscribed to the topic, creating meshes.

As for my scenario with A ↔ Relay ↔ B, A’s message will only get to B if Relay is also subscribed to the topic. So B could request that Relay subscribes to the topic, sending a heartbeat message every so-often to keep Relay propagating those messages to B. I imagine Relay will need some form of rate limiting to help prevent abuse / bandwidth issues.

In the concern of a network with a large percentage of web / non-public nodes behind NATs. Of course dcutr (hole punching) can strengthen web ↔ web connections, but this isn’t 100% successful. In this case I could have web nodes rely on relays like described in the paragraph above.

Additionally, you could use rendezvous servers, DHT or any other peer discovery mechanism to help nodes discover public relays in a way that isn’t simply hard coded. This can also be done to discover nodes interested in a particular topic, strengthening meshes even further.

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