The answer is referential integrity violations in the source data. This is the most likely cause because AWS DMS disables foreign key constraints during the full load phase to maximize throughput, then attempts to re-enable them after the data is loaded; if the source data contains orphaned rows or other referential violations, the re-enablement fails, triggering the 'Failed to add foreign key constraint' error. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding of how DMS handles schema migration and constraint enforcement, often appearing as a trap where candidates mistakenly blame CDC or data type mismatches. Remember that DMS does not validate referential integrity during the load itself—it only checks when constraints are reapplied, so dirty source data is the culprit. Memory tip: DMS stands for “Disable, Migrate, then Scold”—it disables constraints, migrates data, then scolds you if your data is dirty.
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 PostgreSQL database to Amazon Aurora PostgreSQL. To minimize downtime, they plan to use the AWS DMS with change data capture (CDC). During the full load phase, DMS reports an error: 'Failed to add foreign key constraint'. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Referential integrity violations in the source data
Option B is correct because DMS disables foreign key constraints during full load to speed up data transfer, then re-enables them. If the data violates constraints, it fails. Option A is wrong because DMS handles data type conversions automatically. Option C is wrong because CDC is not the issue. Option D is wrong because DMS doesn't require a primary key in the target during full load.
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.
✗
CDC is incompatible with foreign key constraints
Why it's wrong here
CDC works with constraints; the error occurs during full load, not CDC.
✓
Referential integrity violations in the source data
Why this is correct
DMS applies constraints after loading data, and if data violates them, the task fails.
Clue confirmation
The clue words "most likely", "minimum / minimize" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The target table lacks a primary key
Why it's wrong here
DMS can create tables without primary keys during full load.
✗
Data type mismatch between source and target
Why it's wrong here
DMS handles data type conversions and would report a different error.
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: Referential integrity violations in the source data — Option B is correct because DMS disables foreign key constraints during full load to speed up data transfer, then re-enables them. If the data violates constraints, it fails. Option A is wrong because DMS handles data type conversions automatically. Option C is wrong because CDC is not the issue. Option D is wrong because DMS doesn't require a primary key in the target during full load.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "minimum / minimize". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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