1-to-1 connections & possibly hidden nodes

[Fred Hebert]

Another approach that I recall working is one that is cookie-based. Each
cookie you set represents cluster membership, so nodes that share a cookie
will connect to each other.

If you create another node that has a distinct cookie, it won't connect to
anything else. If I recall properly, you can however call
erlang:set_cookie(OtherNode, Cookie) to make a single caller able to use a
distinct cookie to talk to OtherNode, meaning it will connect to it, but
won't be able to transitively forward the connection unless the peer also
shares that cookie.

This lets you use non-hidden nodes that are parts of clusters but still
have them able to privately talk to special nodes by using one-off cookies
that act as a way to wall off connection propagation.

On Mon, Jul 12, 2021 at 2:54 PM Stanislav Ledenev <s.ledenev@REDACTED>
wrote:

> If I understand you correctly, erl -connect_all false is what you need.
>
> пн, 12 июл. 2021 г. в 21:27, Roberto Ostinelli <ostinelli@REDACTED>:
>
>> ...And of course the diagram would be (without the copy-pasta issues):
>>
>> <NODE A in cluster> --------- <NODE C in cluster>
>>         \                     /
>>          \                   /
>>           \                 /
>>           <NODE B in cluster>
>>            *       *       *
>>           *        *        *
>>          *         *         *
>>       <NODE B1> <NODE B2> <NODE B3>
>>
>>
>> On Mon, Jul 12, 2021 at 8:24 PM Roberto Ostinelli <ostinelli@REDACTED>
>> wrote:
>>
>>> All,
>>> Is it possible to have a 1-to-1 connection from a node in a cluster to a
>>> single Erlang node which does _not_ connect to the mesh, but only to a very
>>> specific Erlang node?
>>>
>>> I've go a very CPU-heavy application and am trying to find ways to
>>> offload the CPU computations to Erlang nodes (tha don't need to be in a
>>> cluster, except for a single box they refer to).
>>>
>>> Basically something like this:
>>>
>>> <NODE A in cluster> --------- <NODE B in cluster>
>>>         \                     /
>>>          \                   /
>>>           \                 /
>>>           <NODE B in cluster>
>>>            *       *       *
>>>           *        *        *
>>>          *         *         *
>>>       <NODE B1> <NODE B2> <NODE B>
>>>
>>> The distributed cluster is composed of nodes A, B and C, but nodes B1,
>>> B2 and B3 can communicate directly with node B and that node only. Node B
>>> can offload CPU computations to B1, B2, B3 by sending erlang messages to
>>> them and receive results back.
>>>
>>> Every node in the cluster needs ~50x the CPU power, therefore I'm trying
>>> to avoid having the standard cluster grow so big that it would be
>>> generating way too much noise in a full mesh network (especially since it
>>> really isn't needed).
>>>
>>> I can of course use a simple custom TCP binary channel, but was
>>> wandering if something already exists that I could leverage. I've seen that
>>> hidden nodes "Hidden nodes always establish hidden connections to all other
>>> nodes except for nodes in the same global group" [1] so if I understand
>>> this correctly nodes B1-3 would still connect to A and B, even though the
>>> cluster wouldn't know about them.
>>>
>>> Thank you for any considerations you might have,
>>> r.
>>>
>>>  [1] http://erlang.org/doc/man/erl.html
>>>
>>
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