On 07/09/2012 05:56 PM, Saggi Mizrahi wrote:
I don't think AMQP is a good low level supported protocol as it's a very
complex protocol to set up and support.
Also brokers are known to have their differences in standard implementation
which means supporting them all is a mess.
It looks like the most accepted route is the libvirt route of having a c
library abstracting away client server communication and having more advanced
consumers build protocol specific bridges that may have different support
standards.
On a more personal note, I think brokerless messaging is the way to go in ovirt
because, unlike traditional clustering, worker nodes are not interchangeable so
direct communication is the way to go, rendering brokers pretty much useless.
but brokerless doesn't let multiple consumers which a bus provides?
----- Original Message -----
From: "Adam Litke" <a...@us.ibm.com>
To: "Itamar Heim" <ih...@redhat.com>
Cc: vdsm-devel@lists.fedorahosted.org
Sent: Monday, July 9, 2012 9:56:17 AM
Subject: Re: [vdsm] [RFC] An alternative way to provide a supported interface
-- libvdsm
On Fri, Jul 06, 2012 at 03:53:08PM +0300, Itamar Heim wrote:
On 07/06/2012 01:15 AM, Robert Middleswarth wrote:
On 07/05/2012 04:45 PM, Adam Litke wrote:
On Thu, Jul 05, 2012 at 03:47:42PM -0400, Saggi Mizrahi wrote:
----- Original Message -----
From: "Adam Litke" <a...@us.ibm.com>
To: "Saggi Mizrahi" <smizr...@redhat.com>
Cc: "Anthony Liguori" <anth...@codemonkey.ws>, "VDSM Project
Development" <vdsm-devel@lists.fedorahosted.org>
Sent: Thursday, July 5, 2012 2:34:50 PM
Subject: Re: [RFC] An alternative way to provide a supported
interface -- libvdsm
On Wed, Jun 27, 2012 at 02:50:02PM -0400, Saggi Mizrahi wrote:
The idea of having a supported C API was something I was
thinking
about doing
(But I'd rather use gobject introspection and not schema
generation) But the
problem is not having a C API is using the current XML RPC API
as
it's base
I want to disect this a bit to find out exactly where there
might be
agreement
and disagreement.
C API is a good thing to implement - Agreed.
I also want to use gobject introspection but I don't agree that
using
glib
precludes the use of a formalized schema. My proposal is that
we
write a schema
definition and generate the glib C code from that schema.
I agree that the _current_ xmlrpc API makes a pretty bad base
from
which to
start a supportable API. XMLRPC is a perfectly reasonable
remote/wire protocol
and I think we should continue using it as a base for the next
generation API.
Using a schema will ensure that the new API is well-structured.
There major problems with XML-RPC (and to some extent with REST
as
well) are high call overhead and no two way communication (push
events). Basing on XML-RPC means that we will never be able to
solve
these issues.
I am not sure I am ready to conceed that XML-RPC is too slow for
our
needs. Can
you provide some more detail around this point and possibly
suggest an
alternative that has even lower overhead without sacrificing the
ubiquity and
usability of XML-RPC? As far as the two-way communication point,
what
are the
options besides AMQP/ZeroMQ? Aren't these even worse from an
overhead
perspective than XML-RPC? Regarding two-way communication: you
can
write AMQP
brokers based on the C API and run one on each vdsm host.
Assuming
the C API
supports events, what else would you need?
I personally think that using something like AMQP for inter-node
communication and engine - node would be optimal. With a rest
interface
that just send messages though something like AMQP.
I would also not dismiss AMQP so soon
we want a bug with more than a single listener at engine side
(engine, history db, maybe event correlation service).
collectd as a means for statistics already supports it as well.
I'm for having REST as well, but not sure as main one for a
consumer
like ovirt engine.
I agree that a message bus could be a very useful model of
communication between
ovirt-engine components and multiple vdsm instances. But the
complexities and
dependencies of AMQP do not make it suitable for use as a low-level
API. AMQP
will repel new adopters. Why not establish a libvdsm that is more
minimalist
and can be easily used by everyone? Then AMQP brokers can be built
on top of
the stable API with ease. All AMQP should require of the low-level
API are
standard function calls and an events mechanism.
Thanks
Robert
The current XML-RPC API contains a lot of decencies and
inefficiencies and we
would like to retire it as soon as we possibly can. Engine
would
like us to
move to a message based API and 3rd parties want something
simple
like REST so
it looks like no one actually wants to use XML-RPC. Not even
us.
I am proposing that AMQP brokers and REST APIs could be written
against the
public API. In fact, they need not even live in the vdsm tree
anymore if that
is what we choose. Core vdsm would only be responsible for
providing
libvdsm
and whatever language bindings we want to support.
If we take the libvdsm route, the only reason to even have a
REST
bridge is only to support OSes other then Linux which is
something
I'm not sure we care about at the moment.
That might be true regarding the current in-tree implementation.
However, I can
almost guarantee that someone wanting to write a web GUI on top
of
standalone
vdsm would want a REST API to talk to. But libvdsm makes this
use
case of no
concern to the core vdsm developers.
I do think that having C supportability in our API is a good
idea,
but the
current API should not be used as the base.
Let's _start_ with a schema document that describes today's API
and
then clean
it up. I think that will work better than starting from
scratch.
Once my
schema is written I will post it and we can 'patch' it as a
community
until we
arrive at a 1.0 version we are all happy with.
+1
Ok. Redoubling my efforts to get this done. Describing the
output of
list(True) takes awhile :)
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--
Adam Litke <a...@us.ibm.com>
IBM Linux Technology Center
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