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https://issues.apache.org/jira/browse/DISPATCH-630?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15853836#comment-15853836
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Robbie Gemmell commented on DISPATCH-630:
-----------------------------------------
{quote}
I disagree because what you have here is a "client" that is behaving in an
inconsistent manner. If the client is behaving per the JMS mapping spec, it
MUST set the desired capability, so there is no issue. The notion of a
container id is that it represents a single logical entity ... what you are
describing is an entity that is changing its desires/nature over time.
{quote}
The idea when creating the mechanism was to also consider non-JMS client
connections. For JMS we want to have sole use of the container-id otherwise we
arent really doing what is desired in terms of isolating the links used for
durable subscriptions etc, as non-JMS clients could then be operating on the
same links anyway, allowing the two to interfere with each other. Yes, it would
still stop different JMS connections using the same container-id but that alone
isn't sufficient to entirely satisfy the behaviour desired for JMS that lead to
the mechanism existing in the first place, partly defeating the point.
That said, it was always my assumption that since we can't force anyone to
actually implement this on their server, such situations could arise with
particular servers and it would be the applications/clients choice as to how to
handle that, e.g one option being asserting whether the server offered the
capability or not (though we have yet to put in place a mechanism by which this
could be done by the client, rather than by inspection of the server behaviour
upfront). If the server is going to offer the capability and still permit other
connections to use the container-id, I'm not sure what the client/application
could even do in that case as it wouldnt really be possible to discern the
behaviour it was actually getting at a given time.
{quote}
I think enforcing that a distributed network needs to look up every connection
(and remember every connection) just in case the client is behaving in an
inconsistent manner is too large a burden to place on the server side... and I
can see no use case for providing this support.
{quote}
I dont see how you are going to implement the existing (before this JIRA, but
since incorporated by this JIRA by extending the same mechanism) behaviour
without doing that. For the new MQTT-like behaviour the same may be true (one
slightly different option would be to broadcast arrival of the new connection
and have that sever any existing ones, however that probably doesn't give the
behaviour actually desired by the MQTT spec, and you could risk different
connections at similar time to distributed nodes causing each other to be
disconnected erroneously).
As above, it was always my expectation noone could have enforced these systems
to implement the behaviour. That another somewhat related behaviour has come up
somewhat changes things if they share the same mechanism. Maybe they shouldnt.
{quote}
Again I disagree - The container-id represents a single entity... the behaviour
here should either be undefined or (since the client container has clearly
changed its mind) the server container should respect the most recent wish of
the client. Again, in practice this should never occur as the client will have
a fixed mode of operation (JMS-like, MQTT-like, or doesn't desire sole
connection behaviour).
{quote}
If we were to say 'most recent client behaviour', then if a \[JMS\] connection
requested sole use without dropping existing connections, had that granted, and
then another \[MQTT\] connection is allowed to come along and kick it off
despite this, that seems a unexpected and a little unfair (given it arrived
first, gets dropped anyway, and cant reconnect), and perhaps even somewhat
abusable. Making it unknown behaviour seems undesirable.
Yes having different clients using the same 'clientid' as it were would be
silly when they should be using different ones, but as guarding agaisnt
particualr behaviour when that happens is precisely why the mechanism exists,
so it feels to me it should actually do so and defining it to act otherwise (or
not saying what it does) seems off.
> Detecting connections with the same container-id
> ------------------------------------------------
>
> Key: DISPATCH-630
> URL: https://issues.apache.org/jira/browse/DISPATCH-630
> Project: Qpid Dispatch
> Issue Type: Improvement
> Reporter: Paolo Patierno
> Priority: Minor
>
> Using the router in the EnMasse project and looking into the MQTT
> specification we have the following problem on the current EnMasse
> implemetation.
> The MQTT specification says the following ...
> Let's imagine that a client is connected to the broker with client id "1234"
> and that another client tries to connect with same client id. The broker will
> shut down the connection with first client opening the new one.
> Now with our MQTT support, the MQTT gateway can run as multiple instances
> (multiple pods) so this check can't be executed by the gateway locally
> because a client "1234" could connect to MQTT GW-1 and another client (always
> "1234") could connect to the MQTT GW-2 and the gateways don't know about each
> other. The common point they have is the router network inside EnMasse and
> the fact that for each MQTT client a new AMQP connection is created on the
> other side attaching a link with this name : $mqtt.to.<client-id>
> The following idea came ...
> If during the connection we use a container-id that is equals to the
> client-id, could the router have a feature for detecting connections with
> same container-id and providing a way to close the previous ones ?
> It should be an information shared (and cached ?) by routers in their
> inter-router protocol.
> If not at connection level, maybe at link attachment level ? (when two
> clients attach to the same $mqtt.to.<client-id> link)
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