The answer is that the Elastic Beanstalk environment is in a different VPC or subnet that cannot reach the RDS instance. This is correct because the intermittent ETIMEDOUT errors between Elastic Beanstalk and RDS point to a network-layer connectivity failure rather than an application or database configuration issue; since the same Node.js API works perfectly on-premises, the problem must be in the AWS networking path. On the CompTIA Cloud+ CV0-004 exam, this scenario tests your understanding of VPC architecture, routing, and security group dependencies—a common trap is assuming the security group inbound rule alone is sufficient, when in fact the instances must also have a routable network path across VPCs or subnets. Remember the mnemonic "Route Before Rule": if the route isn't there, the rule never gets checked.
CV0-004 Deployment Practice Question
This CV0-004 practice question tests your understanding of deployment. 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 has a hybrid cloud environment with on-premises servers and AWS. They deploy a new application using AWS Elastic Beanstalk with a load balancer and auto scaling group. The application is a Node.js API that connects to an RDS MySQL database. After deployment, users report that the API returns a '500 Internal Server Error' intermittently. The application logs show 'ETIMEDOUT' errors when connecting to the database. The database is deployed in a private subnet with a security group that allows inbound traffic from the Elastic Beanstalk environment's security group. The database connection string uses the RDS endpoint. The same application works perfectly when deployed on-premises. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Elastic Beanstalk environment is in a different VPC or subnet that cannot reach the RDS instance
The intermittent 'ETIMEDOUT' errors indicate a network connectivity issue between the Elastic Beanstalk environment and the RDS database. Since the application works on-premises, the problem is specific to the AWS networking configuration. The most likely cause is that the Elastic Beanstalk environment is deployed in a different VPC or subnet that lacks routing or a VPC peering connection to reach the RDS instance's private subnet, causing timeouts when the load balancer or auto scaling group instances attempt to connect.
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 connection string uses the wrong port number
Why it's wrong here
The default MySQL port is 3306, which is standard and unlikely to be wrong.
✓
The Elastic Beanstalk environment is in a different VPC or subnet that cannot reach the RDS instance
Why this is correct
Network connectivity between VPCs or subnets is likely misconfigured, causing timeouts.
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 security group attached to the RDS instance does not allow traffic from the Elastic Beanstalk environment
Why it's wrong here
The security group is already configured to allow inbound from the Elastic Beanstalk security group.
✗
The RDS instance is in a failed state and needs to be rebooted
Why it's wrong here
The database is running; ETIMEDOUT indicates network issue, not database failure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume security group misconfiguration is the cause, but Cisco tests the understanding that 'ETIMEDOUT' specifically indicates a network layer reachability problem (routing or VPC isolation) rather than a firewall or authentication issue.
Detailed technical explanation
How to think about this question
Under the hood, 'ETIMEDOUT' is a TCP/IP error that occurs when the client sends a SYN packet but never receives a SYN-ACK within the timeout period (default 20 seconds on Linux). This typically happens when the target IP is unreachable due to missing routes, network ACLs blocking outbound traffic, or the target being in a different VPC without proper peering or transit gateway. In a hybrid cloud scenario, the Elastic Beanstalk environment's auto scaling group may launch instances in public subnets that cannot route to the RDS private subnet unless VPC peering or a NAT gateway is configured correctly.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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 — This question tests Deployment — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Elastic Beanstalk environment is in a different VPC or subnet that cannot reach the RDS instance — The intermittent 'ETIMEDOUT' errors indicate a network connectivity issue between the Elastic Beanstalk environment and the RDS database. Since the application works on-premises, the problem is specific to the AWS networking configuration. The most likely cause is that the Elastic Beanstalk environment is deployed in a different VPC or subnet that lacks routing or a VPC peering connection to reach the RDS instance's private subnet, causing timeouts when the load balancer or auto scaling group instances attempt to connect.
What should I do if I get this CV0-004 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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