[zeromq-dev] Connection refused error exclusively in Dockerized app

Benjamin benjamin.l.cordes at gmail.com
Mon Dec 29 09:44:07 CET 2014

Most likely this is an issue with docker. Inside a container processes
don't know about the outside. You have to specifically mount something
or use the ports flag [1] or ambassadors [2]. Using inproc between
host and container will not work. Containers have process isolation.
Containers map closely to contexts which then use tcp to communicate.

It does make sense combining ZMQ and docker. Unfortunately while
dotcloud has done work with zeromq [2], [3] the docker semantics are
based on HTTP/JSON style communication. Depending on what you're
trying to do, docker might be a lot of overhead.

[1] https://docs.docker.com/installation/mac/#container-port-redirection
[2] https://docs.docker.com/articles/ambassador_pattern_linking/
[3] https://github.com/dotcloud/zerorpc-python
[4] http://www.infoq.com/presentations/Distributed-Systems-with-ZeroMQ-and-gevent

On Mon, Dec 29, 2014 at 9:25 AM, Pieter Hintjens <ph at imatix.com> wrote:
> Is this using the same version of ZeroMQ in both cases?
> On Mon, Dec 29, 2014 at 1:02 AM, Kenneth Adam Miller
> <kennethadammiller at gmail.com> wrote:
>> I found out that doing a socket connection on an inproc that hasn't been
>> bound to yet before is what is causing the error. Strange thing is, in
>> docker this fails with an exception. On my host, it works fine.
>> Does anybody know what the best path forward would be? I basically have a
>> subscriber being launched before the publisher, just as the missed message
>> debugger says I should. Those subscribers make connect calls, but the
>> publisher makes a bind. Every thing works as required on the host. But in
>> docker, it blows up at the connect line.
>> What do I do to get it to work?
>> On Thu, Dec 25, 2014 at 10:51 AM, Kenneth Adam Miller
>> <kennethadammiller at gmail.com> wrote:
>>> I have a dockerized ZMQ instance where I am trying to develop an app. I
>>> have duplicate source both inside the docker instance and at the host level.
>>> I can compile both inside and out with duplicate compiler output and both
>>> compile.
>>> The problem is, there has to be some difference between the docker ubuntu
>>> instance and the host, because when I run the docker ubuntu instance, I get
>>> an error at runtime with my unit tests:
>>> terminate called after throwing an instance of 'zmq::error_t'
>>>   what():  Connection refused
>>> But the unit tests run to completion on the host.
>>> I've debugged it, and put print statements, and I know for certain that
>>> the docker instance is failing at a socket connect call.
>>> sock = new zmq::socket_t(ctxt, ZMQ_SUB);
>>> sock->connect("inproc://something");  //<-- FAILS HERE!
>>> Currently I have some confusion as to why it works this way in the host,
>>> because I have a subscriber connecting to an inproc instance that doesn't
>>> have anything bound at yet, but the missing message problem solver in the
>>> ZMQ guide says start subscribers first and then the publisher. In any case,
>>> it works very well on the host.
>>> Can anybody tell me how to debug a connection refused error?
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