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From Robbie Gemmell <robbie.gemm...@gmail.com>
Subject Re: Qpid AMQP 1.0 - How does it all hang together? - was Re: Qpid Dispatch Router component
Date Wed, 09 Oct 2013 19:56:36 GMT
Adding some more specific bits to what Ted covered in his mail.....though I
now see he just beat me to doing so himself, oh well :P

On 9 October 2013 19:22, Fraser Adams <fraser.adams@blueyonder.co.uk> wrote:

> 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?
>

The engine is effectively an AMQP 1.0 implementation that can be used to
add support to a [potentially existing] product without requiring
implementation of AMQP 1.0 from scrach, e.g. this is what ActiveMQ and Qpid
C++ brokers do for their 1.0 support. Messenger is a form of API for
applications doing messaging that uses the underlying engine as its AMQP
1.0 implementation, and I'll now defer to others to better describe it
beyond that :)


>
> 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?
>

Similar, but not entirely the same, as Qpid::client was the actual C++
client interface for some time but as mentioned was close to the
specification itself, and so a higher level messaging API was later created
to abstract away some of that detail and provide a replacement messaging
API that could allow easier transition to newer protocols. Proton is in
part something that could be used to underneath API X to make it support
AMQP 1.0 (e.g. the qpid messaging API), but there also isnt necessarily a
client API above it at and it could jsut be getting used directly (e.g
possibly with the brokers).


>
>
> 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?).
>

You can stick a broker in the middle and the above just becomes a
client<->broker<->client model like you are used to. Depending on what you
are actually doing though, you might not need or want a broker, and that
field is likely to develop as time goes. For example, brokers can do things
like provide Queues, but that is essentially just something with a name
that accepts your messages...you migiht want to be sending to something
with a name that isnt a queue on a broker.


>
> 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?
>

I think all I would say here would be to echo my points above: you can end
up with something that very closely resembles what you are used to, i.e.
clients talking directly to brokers and using queues and topics, or
depending on your needs you might want to end up with something different.


>
> 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<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.
>
>
The existing AMQP 1.0 JMS 1.1 client was essentially the result of
prototyping work to prove out the 1.0 implementation as it was being
authored, before Proton was conceived. The new client you mention is a
separate implementation getting underway which will support the new JMS 2.0
spec released since then, be built around Proton now that it exists, and
develop in tandem with work to create a documented JMS mapping for AMQP 1.0
within the OASIS AMQP Bindings & Mapping TC. It will indeed eventually
replace the prior 1.0 client.


> 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 <tross@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>
>>> <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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