search

libp2p / go-libp2p-examples

Example libp2p applications
MIT License
338 stars 145 forks source link

chat-with-rendezvous: No way found to remove host from kad-dht #24

Open stefanhans opened 5 years ago

stefanhans commented 5 years ago

The default rendezvousString did not work well for me.

Instead, I use a UUID as rendezvousString and it did work better. But, after a restart, I get errors concerning the old peers:

Using a new UUID, there are no errors.

How can I remove peers from kadDht? I tried it with contexts and methods, but without success. How can it be done?

upperwal commented 5 years ago

@stefanhans So everyone trying this code by default are using meet me here as the rendezvousString.

So every time you run this code a new peer is started and it will announce itself (using Provide) to the bootstrap node with rendezvous point meet me here. But what happens once you disconnect?

Your address is still registered in the bootstrap node at that rendezvous point (till the time it expires and dht is forced to remove it) and anyone looking for new peers to connect (using FindProviders) will get your address. Now bootstrap peers don't know if these address or peers are still alive. Now, when you try to connect to them you get dial attempt failed: error.

Now, this is not your peers fault instead it's the bootstrap peer giving you dead peers. I don't think libp2p has any method which lets you remove peers from the bootstrap peer's list. It should be the bootstrap peer who should ping a remote node just to check if it is alive or dead and act accordingly. RFC: rendezvous is a more sophisticated rendezvous protocol which is better than the existing dht hack.

You might also notice that if you run a peer (let's say A) and announce yourself to the dht and now start another peer (say B) which queries the bootstrap peer for new addresses. All peers received by peer B are dead and none of the address corresponds to peer A. This happens because bootstrap peer returns a random subset of the peers registered with it.

So, it would be better to not use meet me here instead use something unique and start two peers with the same rendezvousString. For meet me here to work you need more number of alive peers than the dead ones.

stefanhans commented 5 years ago

Hi @upperwal,

sounds reasonable 😀 thx

I ended up with using a UUID as rendezvous string. Still not always getting all peers connected in the prototype of mine.

Maybe SWIM(++) protocol from Hashicorp is worth a try.

Cheers, Stefan