The answer is a change in the source database’s security group rules that no longer permits inbound traffic from the Glue job’s IP range. This is correct because a “Connection timed out” error in a JDBC context signals a network-level failure, not an authentication or schema mismatch; since the job ran successfully before, the most likely cause is that the security group for the source database has been modified to block traffic on the JDBC port (e.g., 5432 for PostgreSQL or 3306 for MySQL). On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding that Glue ETL jobs run within a VPC using elastic network interfaces, and connectivity hinges on proper security group and subnet configurations—a common trap is to immediately suspect credential or query issues when the real culprit is network access. Remember the mnemonic “Time Out = Traffic Out” to recall that a timeout almost always points to a firewall or security group blocking the path, not a database-side problem.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. 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 data engineer is troubleshooting a failed AWS Glue ETL job that reads from a JDBC source. The error log shows 'java.sql.SQLException: Connection timed out'. The job previously ran successfully. Which of the following 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group for the source database no longer allows traffic from the Glue job's IP range.
The error 'Connection timed out' indicates a network-level failure, not an authentication or schema issue. Since the job previously ran successfully, the most likely cause is that the security group for the source database no longer allows inbound traffic from the Glue job's IP range. AWS Glue ETL jobs run in a VPC with elastic network interfaces, and the security group rules must permit traffic on the JDBC port (e.g., 5432 for PostgreSQL, 3306 for MySQL).
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 JDBC connection string has incorrect credentials.
Why it's wrong here
Incorrect credentials produce an authentication error, not a timeout.
✗
The source database schema has changed.
Why it's wrong here
Schema changes cause SQL parsing errors, not connection timeouts.
✗
The Glue job's timeout setting is too low.
Why it's wrong here
Job timeout is separate; the error is a connection timeout from the database side.
✓
The security group for the source database no longer allows traffic from the Glue job's IP range.
Why this is correct
A network connectivity issue causes a timeout.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the distinction between authentication errors (wrong credentials) and network connectivity errors (timeout), and candidates may confuse the Glue job timeout setting with a network timeout.
Detailed technical explanation
How to think about this question
The TCP three-way handshake must complete for a JDBC connection to be established; a timeout occurs when the SYN packet is not acknowledged (e.g., due to a firewall dropping the packet). AWS Glue uses elastic network interfaces in the customer's VPC, so the source database's security group must allow inbound traffic from the Glue job's security group or the VPC CIDR. A common real-world scenario is when security group rules are inadvertently removed during a change management process.
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.
Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The security group for the source database no longer allows traffic from the Glue job's IP range. — The error 'Connection timed out' indicates a network-level failure, not an authentication or schema issue. Since the job previously ran successfully, the most likely cause is that the security group for the source database no longer allows inbound traffic from the Glue job's IP range. AWS Glue ETL jobs run in a VPC with elastic network interfaces, and the security group rules must permit traffic on the JDBC port (e.g., 5432 for PostgreSQL, 3306 for MySQL).
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". 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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