Hey all,
The thread below on the dev list has prompted me to ask something that
I've tentatively mentioned before, but am still a bit embarrassed to
raise 'cause it probably makes me seem a bit stupid :-( here goes
anyway.....
So I've kind of held off going down the AMQP 1.0 path partly due to lack
of time, but also partly due to lack of understanding of how it "all
hangs together", the new website helps a bit - but TBH I'm still left
scratching my head somewhat.
I'll try to explain:
Now I know that Proton is intended to be a component usable beyond just
the Qpid "product set", but there's a "protocol engine" and a "messenger
API" and I'm not even that clear on the relationship between the two of
those - for example could one use the protocol engine completely
independently (is there an engine API?) or is the messenger API intended
to be the lowest "unit of currency", what would be the benefit using the
raw engine?
Then beyond that there's the relationship with say qpidd and
qpid::messaging. Now I'm aware that when the Proton libraries are
detected qpidd and qpid::messaging get built with Proton support, I'm
"guessing" that in that case the relationship analogous to that of
qpid::client where qpid::client was the low level AMQP speaking API and
qpid::messaging provides a higher level abstraction, so I *think* that's
the relationship with Proton there - but I'm not sure? Is the proton API
close to the AMQP 1.0 specification in say the way that qpid::client was?
But then there's more nuance, so I'm aware that with AMQP 1.0 there's a
more peer-to-peer relationship and indeed the Proton tests seem to have
msgr-recv and msgr-send talking directly to each other without a broker.
So that leads me to ask the question what's the relationship with the
broker - in other words what services are provided in messenger, what
are enhanced in qpid::messaging and what are layered on top of that via
the broker (and how does the addressing and routing work?).
Some examples of where I'm befuddled include how does subscription work
at a peer to peer level? For example I think that exchange nodes are
only something I've heard discussed in the context of qpidd and
similarly I think the same is true of message selectors, so does Proton
only provide low level network connectivity and data serialisation (and
possibly single client queue) and all the other stuff needed for
connecting a network of clients are part of the broker services.
I suppose what I'm really asking is what "services" are provided at each
"layer" of the Qpid "stack" - clearly you can do useful stuff with just
Proton - but what stuff and what are the limits? What would you then get
from qpid:messaging and what then does the broker throw into the mix.
Are there any diagrams that illustrate this sort of relationship?
The dispatch router adds yet more nuance into the mix. From my (limited)
understanding it seems to offer at least some of the same services as
the broker - but I'm not quite sure what. In my case I've got a very
large federated topology and I have lots of left hand systems feeding in
to fewer systems towards the right. Given that it's only on the right
hand side broker that I have lots of consumers doing complex
subscriptions and the rest of the brokers are employing fairly simple
queue routes I'm thinking that the dispatch router could ultimately be
something to "tidy up" the left hand side of my system - but I'm not
quite sure.
Apologies if these seem silly questions, I'm sure that the answers are
obvious to those who've been involved at the architectural stages, but
ultimately from my perspective the overall holistic architecture isn't
totally clear.
Even at a basic level I've not actually noticed anything in the
programming book
http://qpid.apache.org/releases/qpid-0.24/programming/book/index.html
that seems to mention even how to connect via AMQP 1.0 vice 0.10. I
think that it has been mentioned on the mailing list by Gordon so I'm
sure I could dig the info out, but is it missing from the docs (or am I
just not looking hard enough). On a similar note for Proton the
msgr-send and msgr-recv examples are fine as far as it goes, but I'm
thinking that to figure out how to do anything more complex my best bet
is likely to be to "reverse engineer" the qpid::messaging bindings - I
can't see anything obvious for how to send a map for example. I'm
guessing that Proton is just as erm "nuanced" as qpid::client, so really
powerful and flexible, but you have to know what you're doing to get the
best (say performance) out of it, the API documentation looks pretty
decent to be fair but I'm not sure that's enough to help me drive it
really effectively.
On top of that there seems to be a growing number of JMS clients,
there's the original AMQP 0.10, there's an AMQP 1.0 one in the main Qpid
tree and there's a separate Proton based AMQP 1.0 one that's a separate
component (in a similar vein to Proton). I can see that the increased
modularisation is a good thing and I assume that at some point the
original AMQP 1.0 JMS client will be deprecated in favour of the Proton
based one, but at the moment it's all a bit confusing without anything
that describes the relationship between then. I'm gleaning what little
knowledge I have out of a range of threads on the mailing list and I've
probably missed something.
I'm sorry if this comes across in any way as critical in email form,
it's really not intended to, I'm just keen to finally make a proper
start on my AMQP 1.0 journey and to be honest I feel a little out of my
depth at the moment :-(
Blame Ted for prompting me to write this ;->
Cheers,
Frase
On 09/10/13 17:20, Rob Godfrey wrote:
Hi Ted,
I think before we make this a full sub project, it would be good to have
clarity on exactly the proposed scope of Dispatch, how it is expected to
interact with other components within Qpid, or within wider AMQP networks.
I think in retrospect we didn't do this clearly enough with Proton (for
example).
Moreover I would personally like to understand which AMQP standards it will
be looking to implement, and which not. For instance I notice this line in
the docs for Dispatch:
*Address**Description* /_local/agentThe management agent on the attached
router/container. This address would be used by an endpoint that is a
management client/console/tool wishing to access management data from the
attached container.
Which doesn't seem to conform with the proposed management specification
for AMQP, nor does the document make any mention of how dispatch is to be
managed.
Cheers,
Rob
On 9 October 2013 17:22, Ted Ross <tr...@redhat.com> wrote:
The AMQP Router project (Qpid Dispatch, announced previously on the user
list) is gaining in community interest and is nearing the point where a
first release is appropriate. In preparation for a release, I proposethat
this sub-project follow the lead of both Proton and the AMQP1.0 JMS
projects. This involves:
1. Moving the code from qpid/extras to
http://svn.apache.org/repos/**asf/qpid/dispatch<http://svn.apache.org/repos/asf/qpid/dispatch>
,
2. Requesting, by vote, the creation of a JIRA project to track its
issues and releases.
Unless there are objections, I will move forward with the above two tasks.
Regards,
-Ted
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