Your company currently has a set of applications deployed to Azure. All of the changes are managed via Azure DevOps. The requirements of each application, when it comes to feature releases, are given below.

Application Name

Requirement

testapp1

This is a mission critical application. You have to ensure that a small group of users first opt for testing changes to the application, before the actual change is released.

testapp2

Here you need to minimize the deployment of changes to the application. You should be able to roll back also as quickly as possible.

Which of the following is the release strategy you would opt for testapp1?

Answer options:

A.Blue/Green deployment
B.Canary deployment
C.Rolling deployment
D.Primary deployment

Answer - B 
You can achieve this type of deployment with Canary deployments. Canary deployments are used to deploy changes to a set of users first. Once the users confirm that the application changes are fine, then the complete rollout can be carried out. 
Option A is incorrect because this involves having two environments when it comes to application deployments. 
Option C is incorrect because this involves making rolling deployments to infrastructure. 
Option D is incorrect because this is not a valid deployment model. 
For more information on an example on Canary deployments, one can browse to the following URL- 

https://docs.microsoft.com/en-us/azure/virtual-machines/linux/tutorial-azure-devops-canary-strategy