Service Bus (Maybe?) for web farm

Question

Part of this question is I'm not even sure what exactly I'll need to ask, so I'll start with the situation and work out from there.

One project I'm working on involves use of COMET via the aspComet library. The use case of the program is somewhat of a collaborative slideshow. One person runs the bulk of it, with one or more participants able to perform certain actions. Low latency between when an action is performed on screen

Previously, it was just running on one server. Now, we're wanting to scale it out a bit, more for reliability than performance reasons. So, we have some boxes out in Rackspace's cloud and all that fun stuff.

I knew from the start of this that I was going to need to make some changes to the way the COMET stuff works since different people in the same "show" might be on different servers, and I have no way of knowing what "show" they belong to until after they have already arrived on the site.

I initially tackled this using the WCF Mesh provider, which wasn't well documented to start with, now I'm running into issues with dispatching messages to it sometimes get lost, or delayed (I'm not 100% sure what is going on there), but it screws up the long poll for COMET and breaks things in rather strange ways (Clicking a button may trigger an event, or it'll hang for 10 seconds {long poll duration} and not actually do anything).

More research leads me to believe one of the .Net service bus providers may do what I need. However, I can't find examples that would cover what I need:

1. No single point of failure (outside of a database)
2. No hardcoding of peers.
3. Near-realtime (no polling, event based would be best)

My ideal solution would involve that when a server comes up, it lets other servers know of its existence (Even if it's just a row in a table somewhere), and they can start sending broadcast messages among each other, with each server being both a publisher and subscriber. This is what I somewhat had in the WCF Mesh provider, but I'm not overly confident in that code.

Can anyone point me in the right direction with this? Even proper terms to look for in the docs for service bus providers would be good at this point. Or are service buses not what I want? At this point I would settle for setting up a Jabber server on each web server and use that, if it could fit within my constraints.

Answer 1

I can't speak a ton to NServiceBus, but I expect the answers will be similar.

1. Single point of failure: MSMQ can use multicasting, which means each endpoint will broadcast it's existence and no DB table is needed. RabbitMQ uses this Exchange-to-Queue binding process which means as long as the Rabbit instance or cluster is up then messages still exist. RabbitMQ can be clustered, MSMQ cannot be. *Note: You might have issues with multicasting with Rackspace, no idea how they work. If so, you'll have to fall back on the runtime services for MSMQ (not RabbitMQ), that would create a single point of failure because everyone has a single point to coordinate control messages through.

2. Hard coding of peers: discussed above a bit; MSMQ's multicast handles it. Rabbit it can also be done, just bind queues to an exchange you want to listen to. MassTransit takes care of this for you.

3. Near-realtime: These both use messaging which is near real time. There's no polling in your message consumer code.

I think a service bus seems like a reasonable solution for what you're trying. Some more details would likely be needed, but the general messaging approach is correct. There are other more light weight messaging libraries if you decided you just want something on top of RabbitMQ and configure Rabbit to handle most of the stuff.

To get started with MassTransit, we have documentation up: http://readthedocs.org/projects/masstransit/ and mailing list http://groups.google.com/group/masstransit-discuss. Join the mailing list if you have future questions and someone will try and help you out.