You are planning an upgrade strategy for an existing Azure application. Multiple instances of the
application run in Azure. The management team is concerned about application downtime, due to a
business service level agreement (SLA).
You are evaluating which change in your environment will require downtime.
You need to identify the changes to the environment that will force downtime.
Which change always requires downtime?

A.
Adding an HTTPS endpoint to a web role

B.
Upgrading the hosted service by deploying a new package

C.
Changing the value of a configuration setting

D.
Changing the virtual machine size

Explanation:
If you change the number of endpoints for your service, for example by adding a HTTPS endpoint for
your existing Web Role, it will require downtime.

Re-Deploying your Windows Azure Service without Incurring Downtime
http://blog.toddysm.com/2010/06/re-deploying-your-windows-azure-service-without-incurringdowntime.html