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.
Exhibit
Refer to the exhibit.
```
aws rds create-db-instance-read-replica \
--db-instance-identifier my-read-replica \
--source-db-instance-identifier my-source-db \
--db-instance-class db.r5.large \
--region us-west-2
```
The source DB instance is in us-east-1. The command fails with an error.
A database administrator runs the command shown in the exhibit to create a read replica in us-west-2 from a source DB instance in us-east-1. The command fails. 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.
Exhibit
Refer to the exhibit.
```
aws rds create-db-instance-read-replica \
--db-instance-identifier my-read-replica \
--source-db-instance-identifier my-source-db \
--db-instance-class db.r5.large \
--region us-west-2
```
The source DB instance is in us-east-1. The command fails with an error.
A
The source DB instance does not have backup retention enabled.
Cross-region read replicas require automated backups enabled on the source.
B
The source DB instance is not publicly accessible.
Why wrong: Public accessibility is not required for replication within AWS.
C
The replica instance class db.r5.large is not available in us-west-2.
Why wrong: db.r5.large is generally available in us-west-2.
D
The replica must use the same DB instance class as the source.
Why wrong: Replicas can have different instance classes.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The source DB instance does not have backup retention enabled.
The command fails because creating a cross-Region read replica requires the source DB instance to have automated backups enabled (backup retention period > 0). Without backups, Amazon RDS cannot generate the necessary transaction logs to replicate data to the replica in us-west-2. This is a prerequisite for any read replica creation, whether in the same Region or across Regions.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 source DB instance does not have backup retention enabled.
Why this is correct
Cross-region read replicas require automated backups enabled on the source.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The source DB instance is not publicly accessible.
Why it's wrong here
Public accessibility is not required for replication within AWS.
✗
The replica instance class db.r5.large is not available in us-west-2.
Why it's wrong here
db.r5.large is generally available in us-west-2.
✗
The replica must use the same DB instance class as the source.
Why it's wrong here
Replicas can have different instance classes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the failure is due to instance class availability or public accessibility, overlooking the mandatory backup retention requirement for read replica creation.
Detailed technical explanation
How to think about this question
Under the hood, cross-Region read replicas rely on asynchronous replication using the DB engine's native replication protocol (e.g., MySQL's binlog or PostgreSQL's WAL streaming). The source DB instance must have automated backups enabled to retain the necessary binary logs or WAL segments for the replica to catch up. If backup retention is disabled, the source purges old logs immediately, making it impossible for the replica to synchronize. A real-world scenario is when an administrator disables backups to save storage costs, then later attempts to create a replica and encounters this failure.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Deployment and Migration — This question tests Deployment and Migration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The source DB instance does not have backup retention enabled. — The command fails because creating a cross-Region read replica requires the source DB instance to have automated backups enabled (backup retention period > 0). Without backups, Amazon RDS cannot generate the necessary transaction logs to replicate data to the replica in us-west-2. This is a prerequisite for any read replica creation, whether in the same Region or across Regions.
What should I do if I get this DBS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". 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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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