This DEA-C01 practice question tests your understanding of data store management. 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 using Amazon RDS for PostgreSQL with Multi-AZ deployment. The primary instance fails and a failover occurs. After the failover, the application cannot connect to the database. 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: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The application is using the old primary instance endpoint instead of the RDS CNAME.
After a Multi-AZ failover in Amazon RDS for PostgreSQL, the DNS CNAME record is automatically updated to point to the new primary instance in the standby Availability Zone. If the application is configured with the old primary instance's endpoint (the specific IP or DNS name of the original instance) instead of the RDS CNAME (which remains constant), it will attempt to connect to the failed instance, which is no longer available. This is the most likely cause of connectivity loss because the CNAME is the stable connection point that follows the active primary.
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 database instance is in a 'stopped' state after failover.
Why it's wrong here
After failover, the new primary becomes available.
✗
The Multi-AZ failover requires manual intervention to complete.
Why it's wrong here
Multi-AZ failover is automatic.
✗
The security group for the RDS instance was not updated during failover.
Why it's wrong here
Security groups are attached to the instance, which remains the same.
✓
The application is using the old primary instance endpoint instead of the RDS CNAME.
Why this is correct
The application should use the CNAME, which updates automatically after failover.
Clue confirmation
The clue words "most likely", "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume security groups or instance state are the issue, but AWS explicitly tests the concept that the RDS CNAME is the correct connection target and that hardcoding endpoints leads to failover failures.
Detailed technical explanation
How to think about this question
Under the hood, RDS Multi-AZ uses synchronous replication to a standby in a different AZ, and failover is triggered by a health check or manual reboot with failover. The DNS CNAME (e.g., mydb.xxxxxx.us-east-1.rds.amazonaws.com) is updated within 60–120 seconds to resolve to the new primary's private IP. Applications that hardcode the IP address or use the old instance's DNS name (which becomes stale) will fail to connect, while those using the CNAME experience only a brief outage during DNS propagation.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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.
Data Store Management — This question tests Data Store Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The application is using the old primary instance endpoint instead of the RDS CNAME. — After a Multi-AZ failover in Amazon RDS for PostgreSQL, the DNS CNAME record is automatically updated to point to the new primary instance in the standby Availability Zone. If the application is configured with the old primary instance's endpoint (the specific IP or DNS name of the original instance) instead of the RDS CNAME (which remains constant), it will attempt to connect to the failed instance, which is no longer available. This is the most likely cause of connectivity loss because the CNAME is the stable connection point that follows the active primary.
What should I do if I get this DEA-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", "primary". 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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