- A
The manually added subnet will be removed because the blueprint definition now takes precedence.
Why wrong: This is incorrect. Azure Blueprints use incremental deployment mode, which does not delete resources that exist but are not defined in the blueprint. The manually added subnet is not part of the blueprint definition, so it is not removed.
- B
The manually added subnet will be preserved because blueprints do not manage resources after creation.
This is correct. By default, Azure Blueprints do not actively manage resources after they are deployed. When the blueprint assignment is updated, only the resources defined in the blueprint are added or modified; manually added resources that are not in the blueprint remain unchanged.
- C
The manually added subnet will be overwritten by the updated blueprint definition.
Why wrong: This is incorrect. The updated blueprint definition includes only the original subnets and a new network security group rule; it does not include the manually added subnet. Therefore, it will not be overwritten.
- D
The blueprint update will fail because the subnet already exists.
Why wrong: This is incorrect. The presence of an extra subnet that is not defined in the blueprint does not cause a failure. The blueprint update simply applies its template; existing resources that conflict may cause an error only if the template attempts to create a resource that already exists and the properties are different, but a manually added subnet is not being recreated by the blueprint.
Quick Answer
The answer is that the manually added subnet will be preserved because Azure Blueprints do not manage resources after they are created. This occurs because Blueprints deploy resources using Azure Resource Manager templates in incremental mode by default, meaning an updated assignment only affects resources defined in the blueprint itself—any manually created resources, like the new subnet, remain untouched and are not removed or overwritten. On the Microsoft Azure Fundamentals AZ-900 exam, this scenario tests your understanding of Blueprint behavior versus Azure Policy, with a common trap being the assumption that Blueprints continuously enforce configuration like a policy would. Remember the key distinction: Blueprints are for initial deployment and versioning, not ongoing management of existing resources. A helpful memory tip is to think of Blueprints as a “starter kit” that sets up the environment once, while manual additions are like furniture you bring in later—updating the kit’s instructions won’t remove your furniture.
AZ-900 Describe Azure management and governance Practice Question
This AZ-900 practice question tests your understanding of describe azure management and governance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses Azure Blueprints to enforce a standard landing zone for all development subscriptions. The blueprint includes a virtual network, subnets, and network security groups. After the blueprint is assigned to a subscription, a development team manually adds a new subnet to the virtual network. The company plans to update the blueprint to add a new network security group rule. When the updated blueprint is published and the assignment is updated, what will happen to the manually added subnet?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The manually added subnet will be preserved because blueprints do not manage resources after creation.
Azure Blueprints deploy resources using Azure Resource Manager templates in incremental mode by default. When a blueprint assignment is updated, only the resources defined in the blueprint are affected. Resources that were manually created and are not part of the blueprint definition—such as the manually added subnet—are preserved and not removed or overwritten. To prevent manual modifications, a resource lock can be applied via the blueprint assignment, but that is not the case in this scenario.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The manually added subnet will be removed because the blueprint definition now takes precedence.
Why it's wrong here
This is incorrect. Azure Blueprints use incremental deployment mode, which does not delete resources that exist but are not defined in the blueprint. The manually added subnet is not part of the blueprint definition, so it is not removed.
- ✓
The manually added subnet will be preserved because blueprints do not manage resources after creation.
Why this is correct
This is correct. By default, Azure Blueprints do not actively manage resources after they are deployed. When the blueprint assignment is updated, only the resources defined in the blueprint are added or modified; manually added resources that are not in the blueprint remain unchanged.
Related concept
CIDR notation defines the prefix length.
- ✗
The manually added subnet will be overwritten by the updated blueprint definition.
Why it's wrong here
This is incorrect. The updated blueprint definition includes only the original subnets and a new network security group rule; it does not include the manually added subnet. Therefore, it will not be overwritten.
- ✗
The blueprint update will fail because the subnet already exists.
Why it's wrong here
This is incorrect. The presence of an extra subnet that is not defined in the blueprint does not cause a failure. The blueprint update simply applies its template; existing resources that conflict may cause an error only if the template attempts to create a resource that already exists and the properties are different, but a manually added subnet is not being recreated by the blueprint.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related AZ-900 subnetting questions on CIDR, address ranges, and subnet selection.
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FAQ
Questions learners often ask
What does this AZ-900 question test?
Describe Azure management and governance — This question tests Describe Azure management and governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The manually added subnet will be preserved because blueprints do not manage resources after creation. — Azure Blueprints deploy resources using Azure Resource Manager templates in incremental mode by default. When a blueprint assignment is updated, only the resources defined in the blueprint are affected. Resources that were manually created and are not part of the blueprint definition—such as the manually added subnet—are preserved and not removed or overwritten. To prevent manual modifications, a resource lock can be applied via the blueprint assignment, but that is not the case in this scenario.
What should I do if I get this AZ-900 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related AZ-900 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: May 17, 2026
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