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Re: [Pulp-list] Messaging Questions



This is a really good discussion and I glad you're challenging this. I've already added support for asynchronous request/response (with callback) in the messaging framework. It is very straight forward. I'm just not sure we should use it because having one asynchronous mechanism (Tasks) using another (Messaging) can introduce unwanted complexities. But, If we need to do it to support specific use cases or efficiencies, we certainly can.

On 07/08/2010 09:33 AM, Jason Dobies wrote:
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Yes it does.  If we stick with only synchronous requests to that agent
and leave asynchronous stuff to the pulp Task engine, temporary
(non-durable) queues will be a good approach to pruning dead queues.

This is probably a stupid question, but if we're only doing synchronous
requests

To be clear, I was suggesting synchronous request/response. Asynchronous request (no response) is a different matter because it does not introduce complexity.

and they only go to one agent (or rather, each agent has its
own queue), why are we using a message bus in the first place?I always
viewed it as the benefits of message buses were that they offered a
pub/sub model and were really conducive to asynchronous operations.

Fair question.

We will be using (I think) qpid for more then request/response. I expect we'll want the agent to broadcast (pub/sub) heartbeat messages. Also, on the server-side, we expect to broadcast (pub/sub) events intended for system integration. For example, integration between pulp and candlepin.

Also, message brokers provide queueing, reliable delivery and content based messaging routing (just to name a few).

Maybe asking some other questions will shed some light on whether we need asynchronous request/response (callback) for agent operations.

When asking a large collection of agents to perform an operation:

Is this one async task or a task per consumer (agent)?
Do we need to provide status of this operation for each agent?


- --
Jason Dobies
RHCE# 805008743336126
Freenode: jdob
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