Frase,
This is an excellent post, and I believe quite relevant. I'll try to
address your questions at an abstract level rather than point-by-point.
Your confusion is not unique, but quite justified.
AMQP 1.0 is simply a wire-level protocol specification for symmetric
point-to-point data communication. It has very advanced semantic
capabilities that are inspired by middleware messaging. AMQP is, in my
opinion, a game changer for distributed computing. It opens up
possibilities that go way beyond client/broker messaging. In fact, it
holds the potential to revolutionize the much broader world of data
networking and distributed systems because it offers capabilities that
TCP/IP and HTTP can't touch.
Apache Qpid is the premier open source implementation of AMQP. In the
AMQP 0-{8,9,10} era, Qpid was pretty much just another
middleware-oriented-messaging (MOM) system based on the emerging
standard. With the ratification of AMQP 1.0, which is significantly
different (and superior) to the predecessor specifications, Qpid is
undergoing a bit of a transition.
We have, of course, updated our brokers and clients to use the new
specification and thus continue to serve the MOM use cases.
The Proton project was created for the purpose of promoting AMQP and
making it easy to integrate into many different environments (I believe
we've lost sight of that purpose somewhat).
The Dispatch project was created for the purpose of exploring how AMQP
can be applied in non-broker networks. Dispatch is a form of advanced
interconnect based on AMQP with the goal of building large-scale and
high-performance networks that take advantage of the unique capabilities
of the protocol. It is intended to extend the reach and usefulness of
brokers.
There are a lot of new ideas floating around, some of them overlapping.
I think Qpid is a perfect place to explore and develop new technologies
based on AMQP. This will cause some confusion and force us to work at
articulating what we are doing and thinking, and it will be people like
you who will prompt the important discussions.
Regards,
-Ted
On 10/09/2013 02:22 PM, Fraser Adams 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?
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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