DBS-C01 Deployment and Migration Practice Question
This DBS-C01 practice question tests your understanding of deployment and migration. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 developer needs to deploy an Amazon RDS for MySQL DB instance that is accessible only from a specific EC2 instance in a VPC. Which configuration ensures this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Place the RDS instance in the same VPC as the EC2 instance and configure a security group inbound rule referencing the EC2 security group
Option C is correct because placing the RDS instance in the same VPC and using a security group that allows inbound traffic from the EC2 instance's security group ensures restricted access. Option A is wrong because public accessibility would expose the DB to the internet. Option B is wrong because a network ACL applies at subnet level, not instance level. Option D is wrong because an IAM role does not control network access.
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.
✗
Use an IAM role to allow the EC2 instance to connect to the RDS instance
Why it's wrong here
IAM roles control authentication, not network access.
✗
Enable public accessibility and assign a public IP to the RDS instance
Why it's wrong here
Public accessibility would make the DB accessible from the internet, violating the requirement.
✗
Place RDS and EC2 in different subnets and configure a network ACL
Why it's wrong here
Network ACLs are stateless and not specific to security group-level access.
✓
Place the RDS instance in the same VPC as the EC2 instance and configure a security group inbound rule referencing the EC2 security group
Why this is correct
This ensures traffic is allowed only from the specific EC2 security group.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Deployment and Migration — This question tests Deployment and Migration — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Place the RDS instance in the same VPC as the EC2 instance and configure a security group inbound rule referencing the EC2 security group — Option C is correct because placing the RDS instance in the same VPC and using a security group that allows inbound traffic from the EC2 instance's security group ensures restricted access. Option A is wrong because public accessibility would expose the DB to the internet. Option B is wrong because a network ACL applies at subnet level, not instance level. Option D is wrong because an IAM role does not control network access.
What should I do if I get this DBS-C01 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 DBS-C01 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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Question Discussion
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