- A
The firewall rule allowing traffic on port 5432 is missing or misconfigured.
Why wrong: 'Connection refused' typically means the destination actively refused the connection, which can happen if the port is not open or the service is not running, rather than a firewall block.
- B
The instance is using an outdated SSL certificate.
Why wrong: SSL issues would result in different errors, such as SSL handshake failures or certificate errors, not 'Connection refused'.
- C
The database service is not running or is not listening on port 5432.
'Connection refused' indicates that the destination host is reachable but no service is listening on that port.
- D
The VPC network has no route to the database subnet.
Why wrong: If there were no route, the error would likely be 'Network is unreachable' or 'No route to host'.
Google PCA Ensure solution and operations reliability Practice Question
This PCA practice question tests your understanding of ensure solution and operations reliability. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Refer to the exhibit. An application running on a GCE instance (ID: 1234567890) is unable to connect to a database at 10.0.0.1:5432. The logs show repeated 'Connection refused' errors. 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 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 database service is not running or is not listening on port 5432.
The 'Connection refused' error indicates that the TCP handshake was rejected by the target host, which typically means the database service is not actively listening on port 5432. This is distinct from a firewall block, which would result in a timeout or 'no route to host' error. Since the error is immediate and specific to port 5432, the most likely cause is that the PostgreSQL or other database service is not running or is bound to a different interface/port.
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 firewall rule allowing traffic on port 5432 is missing or misconfigured.
Why it's wrong here
'Connection refused' typically means the destination actively refused the connection, which can happen if the port is not open or the service is not running, rather than a firewall block.
- ✗
The instance is using an outdated SSL certificate.
Why it's wrong here
SSL issues would result in different errors, such as SSL handshake failures or certificate errors, not 'Connection refused'.
- ✓
The database service is not running or is not listening on port 5432.
Why this is correct
'Connection refused' indicates that the destination host is reachable but no service is listening on that port.
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 VPC network has no route to the database subnet.
Why it's wrong here
If there were no route, the error would likely be 'Network is unreachable' or 'No route to host'.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google PCA exams often test the distinction between firewall blocks (timeout) and service unavailability (connection refused), so the trap here is that candidates confuse a missing firewall rule with a service not listening, even though the error messages are fundamentally different.
Detailed technical explanation
How to think about this question
TCP port 5432 is the default for PostgreSQL. When a client receives 'Connection refused', it means the destination host sent a TCP RST (reset) packet in response to the SYN, which occurs when no process is listening on that port. This can happen if the database service crashed, is not started, or is bound to 127.0.0.1 instead of 0.0.0.0 or the correct IP. In GCP, you can verify the listening state with `ss -tlnp | grep 5432` on the database instance.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this PCA question test?
Ensure solution and operations reliability — This question tests Ensure solution and operations reliability — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The database service is not running or is not listening on port 5432. — The 'Connection refused' error indicates that the TCP handshake was rejected by the target host, which typically means the database service is not actively listening on port 5432. This is distinct from a firewall block, which would result in a timeout or 'no route to host' error. Since the error is immediate and specific to port 5432, the most likely cause is that the PostgreSQL or other database service is not running or is bound to a different interface/port.
What should I do if I get this PCA 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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Last reviewed: Jul 4, 2026
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