How to use AF_SO_RAW / AF_SP_RAW to create Zeromq ROUTER / DEALER equivalent?

[yoshuawuyts]

I'm trying to create the following network setup:

 ┌──────────┐   ┌──────────┐   ┌──────────┐
 │  Client  │   │  Client  │   │  Client  │
 ├──────────┤   ├──────────┤   ├──────────┤
 │   REQ    │   │   REQ    │   │   REQ    │
 └──────────┘   └──────────┘   └──────────┘
       │              │              │
       └──────────────┼──────────────┘
                ┌─────▼────┐
                │  ROUTER  │
                ├──────────┤
                │  Broker  │
                ├──────────┤
                │  DEALER  │
                └──────────┘
                      │
       ┌──────────────┼──────────────┐
       │              │              │
 ┌─────▼────┐   ┌─────▼────┐   ┌─────▼────┐
 │   REP    │   │   REP    │   │   REP    │
 ├──────────┤   ├──────────┤   ├──────────┤
 │Service A │   │Service B │   │Service C │
 └──────────┘   └──────────┘   └──────────┘

I was looking how to create zeromq's ROUTER / DEALER in nanomsg and stumbled upon a mailinglist answer on how to achieve this.

Nanomsg's creator gave the following response:

Just use REQs, REPs and a device in the middle. When creating sockets
for the device, use AF_SP_RAW family (AF_SP_RAW+REQ is what's called
DEALER in ZeroMQ parlance, and AF_SO_RAW+REP corresponds to ROUTER).

This was slightly confusing to me, as I'm not very familiar with the _RAW variants in nanomsg. So my question is: how can I create a ROUTER / DEALER setup in node-nanomsg? Thanks!

[yoshuawuyts]

Ah, so it appears load balancing is built into REQ and PUSH sockets, which clarifies the idea behind it a little; we no longer have to think about how to round robin (or in this case, have a multi-tier round robin) to balance the load. All that I'm curious about now is how to wire up the sockets so they're actually connected (which is a lot more trivial).

• http://250bpm.com/blog:14

[reqshark]

hey that's a good link, i'm also a fan of: http://250bpm.wdfiles.com/local--files/publications/ietf.pdf

Ah, so it appears load balancing is built into REQ and PUSH sockets

that's right, REQ/REP was designed around the need to distribute precise load balancing tasks among stateless workers. There's also PUSH/PULL, discussed some in #118.

@yoshuawuyts, i think RAW sockets usually need sudo permissions like the low ports, but I'm not 100% if that's the case on every operating system and for every AF_SP_RAW combo

[reqshark]

OK I think we only use RAW sockets at the local proxy endpoint, Martin says it's intended for nn_device() which is basically zmq_proxy() or xpub/xsub, etc. from zeromq

here's the better answer: http://www.freelists.org/post/nanomsg/AF-SP-RAW-vs-AF-SP,1

[yoshuawuyts]

Ah right, so nano.device / nano.createDevice is exposed but not mentioned in the documentation. Mentioning stuff like nano.term() might be good to have in there.

It appears there's some tests around device and raw: true:

• unidirectional device
• bidirectional device

raw: true sockets should work with transports other than inproc too right?

edit: I would assume so. From the page you linked:

Use standard sockets if you are going to use the socket yourself. Use RAW sockets to be passed to nn_device().

I think this is pretty clear now; perhaps adding an example for this in /examples might be useful. Thanks!

[reqshark]

yes it would definitely be useful, @yoshuawuyts would you be up for a PR?