You have a current Clouformation template defined in AWS. You need to change the current alarm threshold defined in the Cloudwatch alarm. How can you achieve this?

Answer options:

A.Currently, there is no option to change what is already defined in CloudFormation templates.
B.Update the template and then update the stack with the new template. Automatically all resources will be changed in the stack.
C.Update the template and then update the stack with the new template. Only those resources that need to be changed will be changed. All other resources which do not need to be changed will remain as they are.
D.Delete the current CloudFormation template. Create a new one that will update the current resources.

Answer – C
Option A is incorrect because CloudFormation templates have the option to update resources.
Option B is incorrect because only those resources that need to be changed as part of the stack update are actually updated.
Option D is incorrect because deleting the stack is not ideal when you already have a change option available.
When you need to make changes to a stack`s settings or change its resources, you update the stack instead of deleting it and creating a new stack. For example, if you have a stack with an EC2 instance, you can update the stack to change its AMI ID.When you update a stack, you submit changes, such as new input parameter values or an updated template. AWS CloudFormation compares the changes you submit with the current state of your stack and updates only the changed resources.
For more information on stack updates, please refer to the below link:
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks.html