Question

I was wondering about the best practices in synchronizing multiple azure instances that run the same role.
More precisely, I want to prevent several worker roles to work on the same work-unit.

Azure queues do not seem to help on this matter.
One option is to use an sql table with locks and stored procedures; but using sql synchronization in Azure seems a bit awkward.

Any ideas?

Edit, my detailed(but simplified problem) is as follows:

• There are n targets.
• A unit of work must be done on each target at a specified interval (say 30 seconds – but it is different for each target).
• I have m workers (hosted in h instances).
• Processing a unit of work could take anything between 10 seconds and 1 hour.

The idea is that I have a scheduler that puts units of work in an Azure queue, and each of the m workers will read these and process them.

The problem:

• worker1 starts working on unit1 (which is regarding target1) – this one will take long, say 10 minutes
• 30 seconds pass
• the scheduler puts another unit of work for target1, say unit13
• worker2 starts working on unit13, against the same target1 – not good

I have some ideas, but they don’t seem cloudy enough, so I am interested to see what solutions would you apply for this problem.

Answer 1

I’ve just written a couple blog posts about using blob leases to do this sort of thing. See http://blog.smarx.com/posts/managing-concurrency-in-windows-azure-with-leases and http://blog.smarx.com/posts/building-a-task-scheduler-in-windows-azure.