DBS-C01 Deployment and Migration Practice Question
This DBS-C01 practice question tests your understanding of deployment and migration. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 is migrating a 200 GB PostgreSQL database to Amazon Aurora PostgreSQL. They want to use the AWS DMS console to create a migration task. The source database is in a VPC and the target Aurora cluster is in the same VPC. The DMS replication instance is also in the same VPC. The source database is publicly accessible. What additional configuration is required to enable connectivity between DMS and the source database?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the source database's security group to allow inbound traffic from the DMS replication instance's security group.
Option D is correct because even though the source is publicly accessible, DMS is in a VPC and cannot directly access public IPs unless the VPC has an internet gateway and the route table allows it. The security group of the source must allow inbound traffic from the DMS replication instance's security group. Option A is wrong because DMS does not require a VPC endpoint for source connectivity. Option B is wrong because the replication instance subnet group is already set. Option C is wrong because the source database should not be in public subnet; it can be private with proper routing.
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.
✗
Associate the DMS replication instance with a subnet group that includes public subnets.
Why it's wrong here
Subnet group is already set; the issue is about network connectivity.
✗
Place the source database in the same public subnet as the DMS replication instance.
Why it's wrong here
It's not necessary to change subnet; connectivity can be achieved via routing and security groups.
✗
Create a VPC endpoint for the source database service.
Why it's wrong here
VPC endpoints are for accessing AWS services, not on-premises or publicly accessible databases.
✓
Configure the source database's security group to allow inbound traffic from the DMS replication instance's security group.
Why this is correct
The security group must allow traffic from DMS to reach the database.
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: Configure the source database's security group to allow inbound traffic from the DMS replication instance's security group. — Option D is correct because even though the source is publicly accessible, DMS is in a VPC and cannot directly access public IPs unless the VPC has an internet gateway and the route table allows it. The security group of the source must allow inbound traffic from the DMS replication instance's security group. Option A is wrong because DMS does not require a VPC endpoint for source connectivity. Option B is wrong because the replication instance subnet group is already set. Option C is wrong because the source database should not be in public subnet; it can be private with proper routing.
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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