[erlang-questions] Erlang nodes, connections and sockets

David Welton <>
Mon Mar 3 12:05:04 CET 2014


Hi,

> What do you mean exactly by "sometimes J does not receive messages from E"?
> Does it happen haphazardly, during the same "session"? Does it happen with
> the J epmd running?

I'm not 100% sure, as this was on the Java end.  I don't think the
pattern was super obvious though.

> For two nodes to connect, they have to know about each other, which is why
> epmd exists. If the nodes are connected, epmd is no longer required, the
> existing connection is used. As you discovered, epmd must run on the machine
> where the target of the first connection attempt runs.
>
> Without a "J epmd", if the first contact is initiated by E, then J is not
> found. But if J makes a contact after that, then subsequent E->J works fine
> because the connection has been established.
>
> If there is some network hick-up that makes the J node look disconnected or
> the tablet goes to sleep, then E forgets about it and what happens next
> depends again on who initiates the contact first.
>
> I hope I explained it clearly enough.

Yes, that's how I had surmised things work, but I wanted to confirm
that my mental model reflected reality!

Thank you for the explanation,
-- 
David N. Welton

http://www.welton.it/davidw/

http://www.dedasys.com/



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