The answer is to run the 'Stop task' command with the '--apply-immediately' option before stopping the source database. This is correct because AWS DMS caches ongoing changes in memory during CDC replication, and simply stopping the source database does not flush those cached transactions to the target; the '--apply-immediately' flag forces DMS to write all remaining buffered changes before the task halts, ensuring no transactions are lost. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of DMS cutover procedures and the critical distinction between a healthy task status and the actual application of cached data—a common trap is assuming a healthy status means all changes are already applied. Remember the memory tip: "Stop with apply, or data will fly away" to recall that you must explicitly apply remaining changes during cutover to prevent missing transactions.
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 2 TB Oracle database running on an on-premises Linux server to Amazon RDS for Oracle. The migration must have minimal downtime and must be fully reversible if any issues arise. The DBA has configured AWS DMS with a full load and ongoing replication task. The full load completes successfully, and CDC is replicating changes. During the cutover window, the DBA stops the source database and promotes the target RDS instance. However, after cutover, the application team reports that some recent transactions are missing from the target database. The DBA confirms that the DMS task showed a 'healthy' status before stopping. Which action should the DBA take to resolve the issue and prevent recurrence?
Rebuild the entire migration using a native Oracle export/import tool.
Why wrong: This approach would cause significant downtime and does not prevent recurrence.
B
Increase the replication instance size to improve throughput.
Why wrong: Performance is not the issue; the issue is that the task did not capture all changes before stopping.
C
Restart the DMS task from the beginning to recapture the missing data.
Why wrong: Restarting does not recover the missing transactions because the source is already stopped.
D
Before stopping the source database, run the 'Stop task' command with the '--apply-immediately' option to ensure all cached changes are written to the target.
This ensures that all remaining CDC changes are applied before stopping.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Before stopping the source database, run the 'Stop task' command with the '--apply-immediately' option to ensure all cached changes are written to the target.
Option B is correct. In a DMS migration, the final step should be to capture remaining changes after stopping the source database. This is done by running the 'Stop task' command with the '--apply-immediately' flag or by using the 'Last Stop' command in the console. Option A is wrong because increasing the replication instance size does not address missing transactions. Option C is wrong because restarting the task does not capture the missed transactions; they were already lost. Option D is wrong because rebuilding the migration from scratch is time-consuming and does not address the root cause.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Rebuild the entire migration using a native Oracle export/import tool.
Why it's wrong here
This approach would cause significant downtime and does not prevent recurrence.
✗
Increase the replication instance size to improve throughput.
Why it's wrong here
Performance is not the issue; the issue is that the task did not capture all changes before stopping.
✗
Restart the DMS task from the beginning to recapture the missing data.
Why it's wrong here
Restarting does not recover the missing transactions because the source is already stopped.
✓
Before stopping the source database, run the 'Stop task' command with the '--apply-immediately' option to ensure all cached changes are written to the target.
Why this is correct
This ensures that all remaining CDC changes are applied before stopping.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Deployment and Migration — This question tests Deployment and Migration — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Before stopping the source database, run the 'Stop task' command with the '--apply-immediately' option to ensure all cached changes are written to the target. — Option B is correct. In a DMS migration, the final step should be to capture remaining changes after stopping the source database. This is done by running the 'Stop task' command with the '--apply-immediately' flag or by using the 'Last Stop' command in the console. Option A is wrong because increasing the replication instance size does not address missing transactions. Option C is wrong because restarting the task does not capture the missed transactions; they were already lost. Option D is wrong because rebuilding the migration from scratch is time-consuming and does not address the root cause.
What should I do if I get this DBS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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