windows - Is it a good idea to reuse an Azure web role for backend processing?

Question

I'm porting a huge application to Windows Azure. It will have a web service frontend and a processing backend. So far I thought I would use web roles for servicing client requests and worker roles for backend processing.

Managing two kinds of roles seems problematic - I'll need to decide how to scale two kinds of roles and also I'll need several (at least two) instances of each to ensure reasonable fault tolerance and this will slightly increase operational costs. Also in my application client requests are rather lightweight and backend processing is heavyweight, so I'd expect that backend processing would consume far more processing power than servicing client requests.

This is why I'm thinking of using web roles for everything - just spawn threads and do both servicing requests and backend processing in each instance. This will make the role more complicated but will I guess simplify management. I'll have more instances of a uniform role and better fault tolerance.

Is it a good idea to reuse web roles for backend processing? What drawbacks should I expect?

Answer 1

Sounds like you already have a pretty good idea of what to think about when using multiple roles:

• Cost for 2 instances to meet SLA (although some background tasks really don't need SLA if the end user doesn't see the impact)
• Separate scale units

However: If you run everything in one role, then everything scales together. If, say, you have an administrative web site on port 8000, you might have difficulty reaching it if your user base is slamming the main site on port 80 with traffic.

I blogged about combining web and worker roles, here, which goes into a bit more detail along what we're discussing here. Also, as of some time in March, the restriction of 5 endpoints per role was lifted - see my blog post here for just how far you can push endpoints now. Having this less-restrictive endpoint model really opens up new possibilities for single-role deployments.