[openstack-dev] [oslo.messaging][zeromq] introduce Request-Reply pattern to improve the stability

ozamiatin ozamiatin at mirantis.com
Mon Mar 30 08:02:54 UTC 2015


Sorry for not replying on [1] comments too long.
I'm almost ready to return to the spec with updates.

The main lack of current zmq-driver implementation is that
it manually implements REQ/REP on top of PUSH/PULL.

It results in:

1. PUSH/PULL is one way directed socket (reply needs another connection)
     We need to support backwards socket pipeline (two pipelines). In 
     we have it all in one socket pipeline.

2. Supporting delivery of reply over second pipeline (REQ/REP state 

I would like to propose such socket pipeline:
rpc_client(REQ(tcp)) <=> proxy_frontend(ROUTER(tcp)) <=> 
proxy_backend(DEALER(ipc)) <=> rpc_server(REP(ipc))

ROUTER and DEALER are asynchronous substitution for REQ/REP for building 
1-N and N-N
topologies, and they don't break the pattern.

Recommended pipeline nicely matches for CALL.
However CAST can also be implemented over REQ/REP, using
reply as message delivery acknowledgement, but not returning it to caller.
Listening to reply for CAST in background thread keeps it async as well.

Oleksii Zamiatin

On 30.03.15 06:39, Li Ma wrote:
> Hi all,
> I'd like to propose a simple but straightforward method to improve the
> stability of the current implementation.
> Here's the current implementation:
> receiver(PULL(tcp)) <-- service(PUSH(tcp))
> receiver(PUB(ipc)) --> service(SUB(ipc))
> receiver(PUSH(ipc)) --> service(PULL(ipc))
> Actually, as far as I know, the local IPC method is much more stable
> than network. I'd like to switch PULL/PUSH to REP/REQ for TCP
> communication.
> The change is very simple but effective for stable network
> communication. I cannot apply the patch for our production systems. I
> tried it in my lab, and it works well.
> I know there's another blueprint for REP/REQ pattern [1], but it's not
> the same, I think.
> I'd like to discuss it about how to take advantage of REP/REQ of zeromq.
> [1] https://review.openstack.org/#/c/154094/2/specs/kilo/zmq-req-rep-call.rst
> Best regards,

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