web role and sql azure disaster recovery

Question

I'm working on a quiet large and critical application. It's been deployed to azure with 3 web roles and sql azure db.

In case of disaster, we need to be able to restore both web roles and sql azure to different data centers. Could someone please help me how we can restore SQL Azure DB and Web Role(s) to different data center.

Answer 1

The simple answer is that you take regular backups of your SQL Azure database, which can be restored to a database in another datacenter. You will have a problem with the data since the last backup being lost, which becomes a more difficult problem to resolve — the simplest may be to have a hot standby and use SQL Database Data Sync, but it may not be practical for all the data. Web roles are easier — you redeploy them somewhere else, and change the connection strings to the database. You would also have to change the CNAME for your domain as they will be restored to a different cloudapp.net name.

You did ask for restore, and not failover, right? Performing a failover (where you have a hot standby) is a more difficult problem, particularly as far as data synchronisation is concerned.

I would go back and question 'disaster' and correlate with known facts. I am not sure of the outage history of Azure in specific data centres, but there have been significant Azure-wide outages (leap year 2012 and the certificate problem this year). The ability to restore to a different Azure datacentre won't help you in these scenarios. (Although AWS seems to mostly have regional outages) I don't think that a datacenter-specific recovery strategy is necessary on Windows Azure, but you may want to check the history and likelihood of datacenter-specific failures before making a final call. Having a multi-region architecture that distributes load and data across datacentres, and handles live traffic across all (say using traffic manager), has many benefits — of side effect being builtin-disaster recovery - but comes at an architectural, development, hosting and bandwidth cost.

Go back and write the business case for your datacenter disaster recovery scenario. You may find that it is not worth it financially, or doesn't solve your real problem.