I’ve got a working Silverlight/WCF application that I need to start thinking about scaling.

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Asked: June 9, 20262026-06-09T15:19:46+00:00 2026-06-09T15:19:46+00:00

I’ve got a working Silverlight/WCF application that I need to start thinking about scaling.

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I’ve got a working Silverlight/WCF application that I need to start thinking about scaling. An obvious target for scaling, of course, is Azure.

The key architectural feature of the application is that 2-10 Silverlight clients will join a given “room” (using a duplex Net.TCP connection), and any of those clients can then send a message (for instance, a chat message), which then needs to be pushed in real-time to every other client connected to the same room, using the underlying duplex WCF connection.

Right now, the way the WCF service works is basically to keep in-memory a list of sessions and the rooms that they’re associated with, so that when a message from one session comes in, it can automatically send the message to every other session in the room.

This works fine for a single WCF server instance, but it gets complicated if you need to scale it so that multiple WCF instances are in play. If you use network-layer load balancing, of course, you would typically find that only some of the members of your room are on the same server you’re on, which means that when it comes time to push out messages to all those members, only some of them would actually get notified.

Apart from Azure, I had been thinking that I would handle it via some sort of application-layer load balancing. For instance, the web server that each client downloads the Silverlight application from might do a primitive round-robin sort of load-balancing, i.e., “OK, everyone in room x, you use WCF instance 1. Everyone in room y, you use WCF instance 2.” That sort of thing.

So I have two questions:

(1) Is there any other, better way to architect this, so as to be able to use network-layer load balancing rather than needing to make the application aware of the underlying infrastructure?

(2) If I have to do the application-layer load balancing, what’s the best way to handle this in Azure? Do I have to use the IAAS (full VM’s), or is there a way to do this using PAAS (worker roles)? My understanding is that it’s not possible to independently address worker roles, which would make a roles-based approach difficult, if not impossible.