DEA-C01 Data Ingestion and Transformation Practice Question
A company uses AWS Glue to run ETL jobs that process data from Amazon RDS for MySQL and load it into Amazon S3. The job runs daily and processes incremental changes using the JDBC connection. Recently, the job has been failing with a 'Communications link failure' error. The RDS instance is in a private subnet. Which step should the engineer take first to diagnose the issue?
⚠ Common exam trap
The trap here is that candidates often jump to IAM permissions or JDBC driver issues first, but the 'Communications link failure' error is a classic network connectivity symptom that requires checking security groups and network ACLs before anything else.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the security group and network ACL rules for the RDS instance and the Glue connection.
The 'Communications link failure' error typically indicates a network connectivity issue between AWS Glue and the RDS instance. Since the RDS instance is in a private subnet, the Glue job must be able to reach it via a VPC endpoint or a Glue connection that uses network configuration. Checking the security group (inbound rules for the RDS instance allowing traffic from Glue's elastic network interfaces) and network ACLs (ensuring ephemeral ports are open) is the first logical step to diagnose connectivity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Verify that the IAM role used by Glue has the correct permissions to access RDS.
Why it's wrong here
IAM permissions govern authorisation, not network reachability; a permissions failure returns an access-denied error, not a dropped TCP connection. It is tempting because Glue needs an IAM role to read RDS, and that role would be the correct focus if the job failed with an authorisation error rather than a communications failure.
- ✗
Change the Glue job type from Spark to Python shell.
Why it's wrong here
Python shell jobs cannot use the Glue JDBC connection framework or run Spark ETL, so switching job type removes the mechanism the job needs and cannot resolve a TCP-level failure. It is tempting because Python shell suits lightweight, non-Spark tasks, and would be the right choice for small scripts that do not require distributed processing.
- ✓
Check the security group and network ACL rules for the RDS instance and the Glue connection.
Why this is correct
A 'Communications link failure' means the JDBC connection cannot reach the private RDS endpoint. Verifying security group and network ACL rules for both the RDS instance and the Glue connection confirms whether the required port and subnet traffic are actually permitted.
- ✗
Check that the JDBC driver is compatible with the Glue version.
Why it's wrong here
A JDBC driver incompatibility typically surfaces as class-loading or handshake errors, not a 'Communications link failure' indicating the TCP connection was dropped. It is tempting because driver version mismatches do cause connection errors, and checking compatibility would be correct if the job failed immediately with a driver-related exception.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.