CV0-004 Troubleshooting Practice Question
A company's application is unable to connect to a managed cloud database. The database is deployed in a VPC with public accessibility disabled. The application runs on an EC2 instance in the same VPC. Which three troubleshooting steps should the administrator take? (Choose three.)
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 network ACL associated with the database subnet for appropriate rules.
Options B, C, and E are correct. Option A is incorrect because an internet gateway is not needed for communication within the same VPC. Option D is incorrect because a public IP is not required for instances in the same VPC. Option B checks network ACL rules for the database subnet, which can affect inbound/outbound traffic. Option C verifies the database endpoint configuration in the application, which could be misconfigured. Option E checks the security group for the database, ensuring it allows inbound traffic from the EC2 instance's security group.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Ensure the VPC has an internet gateway attached.
Why it's wrong here
Incorrect. An internet gateway is not needed for communication within the same VPC.
- ✓
Check the network ACL associated with the database subnet for appropriate rules.
Why this is correct
Correct. Network ACLs control traffic at the subnet level and could block the connection.
- ✓
Verify that the database endpoint is correctly configured in the application.
Why this is correct
Correct. A misconfigured database endpoint would prevent the application from connecting.
- ✗
Verify that the EC2 instance has a public IP address.
Why it's wrong here
Incorrect. A public IP is not required for communication within the same VPC.
- ✓
Check the security group for the database to ensure it allows inbound traffic from the EC2 instance's security group.
Why this is correct
Correct. The database security group must allow inbound traffic from the EC2 instance's security group.
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Same concept, more angles
2 more ways this is tested on CV0-004
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company has a three-tier application in a cloud VPC: web servers in a public subnet, application servers in a private subnet, and database servers in a private subnet. The web servers can connect to the application servers, but the application servers cannot connect to the database servers. The security groups are configured as follows: - Web SG: inbound HTTP from 0.0.0.0/0, outbound all - App SG: inbound HTTP from Web SG, outbound all - DB SG: inbound MySQL from App SG, outbound all What is the most likely cause of the connectivity issue?
medium- A.The database security group is missing an inbound rule for MySQL.
- B.The application security group is missing an outbound rule for MySQL.
- ✓ C.The network access control list (NACL) on the database subnet is blocking inbound traffic from the application subnet.
- D.The web security group is blocking traffic to the database.
Why C: Security groups are stateful and allow return traffic automatically, so outbound rules are not the issue. The inbound rule on DB SG allows MySQL from App SG, so A is not the issue. B is not needed because outbound is all. D is irrelevant because web SG does not affect traffic between app and DB. The issue likely is a network ACL (NACL) on the database subnet, which is stateless and needs explicit inbound and outbound rules; if it blocks inbound MySQL from the app subnet, the connection fails.
Variation 2. Refer to the exhibit. An application running on an EC2 instance is failing to connect to an RDS database. What is the most likely issue?
easy- A.The database instance is in a different VPC
- ✓ B.The security group for the RDS instance does not allow inbound traffic from the EC2 instance
- C.The database instance is stopped
- D.The application is using the wrong database port
Why B: A 'connection refused' error typically indicates that the database is reachable but the port is blocked, likely by a security group. Option A is wrong if the database is in a different VPC, the error would be timeout or no route. Option C is wrong because a stopped database would result in a 'no route to host' or timeout. Option D is wrong because port 3306 is standard for MySQL and the error is not about wrong port.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.