How can we choose how many upgrade domains we need for scalability purpose in Windows Azure?

Question

This question is for : Exam 70-487 (Developing Windows Azure and Web Services)

The question is:

You are developing a Microsoft Azure web application. The application will be deployed to
10 web role instances. A minimum of 8 running instances is needed to meet scaling
requirements.
You need to configure the application so that upgrades are performed as quickly as
possible, but do not violate scaling requirements.
How many upgrade domains should you use?

The Options are

A. 1
B. 2
C. 5
D. 10

My question is what will be the correct answer and why? How we are arriving at the solution to the problem statement.

Thanks

Answer 1

Based on my understanding of upgrade domains, the correct answer is 5.

5 upgrade domains and 10 instances means each domain containing 2 instances. As we know updating a Cloud Service involves updating one upgrade domain at a time. With 5 upgrade domains that would mean 2 of the instances will be updated while remaining 8 will keep on working.

Answer 2

The default number of upgrade domains is 5. I found this read quite useful. https://docs.microsoft.com/en-us/azure/cloud-services/cloud-services-update-azure-service

Answer 3

I also think the correct answer is 5.

You have 10 web role instances. If you use 5 update domains you will have this distribution:

WR - UD
1 - 0
2 - 1
3 - 2
4 - 3
5 - 4
6 - 0
7 - 1
8 - 2
9 - 3
10 - 4

So, when the system will update the domain #0, worker role #1 and #6 will be down but you still will have 8 running worker role instances.

https://docs.microsoft.com/en-us/azure/cloud-services/cloud-services-update-azure-service