DEA-C01 Data Operations and Support Practice Question
A data pipeline uses AWS Glue ETL jobs to process data from Amazon RDS for MySQL to Amazon S3. Recently, the jobs have been failing with the error 'Communications link failure' during the connection phase. The RDS instance is in a private subnet, and the Glue job uses a VPC endpoint for S3. What is the most likely cause?
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
✓
The Glue job does not have a network path to the RDS instance because it is not attached to the same VPC subnet.
The 'Communications link failure' error during connection indicates a network connectivity issue between the AWS Glue job and the RDS instance. Even if the Glue job uses a VPC endpoint for S3, that endpoint does not provide connectivity to RDS. To connect to an RDS instance in a private subnet, the Glue job must be attached to the same VPC (e.g., via an elastic network interface) or have a network path through VPC peering or VPN. Option A (max connections) would yield a 'too many connections' error, not a communications link failure. Option B (KMS permissions) would cause an access denied error, not a connection failure. Option C (JDBC driver incompatibility) would typically produce a 'No suitable driver' or driver class not found error. Therefore, the most likely cause is that the Glue job lacks a network path to the RDS instance.
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 RDS database has reached the maximum number of connections.
Why it's wrong here
That error would be 'too many connections', not 'communications link failure'.
- ✗
The Glue job does not have IAM permissions to decrypt the RDS database using AWS KMS.
Why it's wrong here
KMS issues cause access denied, not connection failure.
- ✗
The JDBC driver used by Glue is incompatible with the MySQL version.
Why it's wrong here
An incompatible driver would give a different error.
- ✓
The Glue job does not have a network path to the RDS instance because it is not attached to the same VPC subnet.
Why this is correct
Glue jobs need an ENI in the same VPC to connect to RDS.
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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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.