2021년 12월 3일 (금) 오후 7:39, Piotr Kliczewski <pkliczew@redhat.com>님이 작성:
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> On Fri, Dec 3, 2021 at 11:22 AM Henry lol <pub.virtualization@gmail.com> wrote:
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>> In my understanding, an internal broker was introduced with benefits and enough to cover the workload, right?
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> In general it is correct. There is no broker process running but rather the code is spread between the client (engine) and server (vdsm).
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>> but not clear about the need for it on oVirt because I'm not sure there are so many message flows(or message topics).
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> We created a topic per type of interactions (commands) that are being called. Good number of them are defined.
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>> I felt like it acts as just a proxy only between engine and rpc server, so it looks more desirable to me to directly communicate without message queues in the middle.
>> (even internal broker is coupled with vdsm)
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> We were concerned about topology complexity and never decided to use an external (proxy) broker. The transport communication hides details so from a logic perspective it
> looks like direct communication. Please remember that in the past transport was fully synchronous and one of the requirements was to abstract async so the business layer
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yeah as you said, the business layer can focus on their own logic
thanks to the transport layer.
I thought that the transport layer could be also abstracted and
implemented from raw tcp or websocket, and at first that using msg
protocol with the broker is just an additional overhead. (correct me
if i'm wrong)
(i.e. json-rpc communication through tcp or websocket)
During the transition process we had several protocols being supported so the abstractions are
there. Raw tcp is there and you can implement "just" json-rpc on top of it. In the past we were using xmlrpc
so with this approach you would have unidirectional communication and no notifications.
It was our starting point with the transport changes we did.
but as Artur said, the main reason for using stomp here seems to
easily propagate and define msg flows, right?
There is more to it. We use stomp
heartbeats to determine if a host is healthy. It is used to trigger fencing flow when the host is not reachable.
sorry again in advance if it sounds foolish.
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>> could I know usecases of it in oVirt compared to raw tcp?
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> Interesting one is bidirectional notifications which need to be delivered to specific parts of the logic on either side.
> For most of use cases we could get away with raw tcp.
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>> sorry in advance if it sounds foolish.