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Question 113 of 999

Building and testing applications →hardMultiple ChoiceObjective-mapped

Troubleshooting Cloud Build 'connection refused' Error

This PCD practice question tests your understanding of building and testing applications. 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.

During a Cloud Build run, a developer sees the error: "Step #0: error: failed to fetch metadata: connection refused". The build is trying to access a private Docker registry in a different project. 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.

A
The registry does not exist
Why wrong: If the registry doesn't exist, you'd get a name resolution or 404 error, not 'connection refused'.
B
The build environment cannot reach the registry due to network restrictions
Connection refused typically means the target is actively refusing the connection, often due to firewalls or VPC Service Controls preventing access.
C
The build service account lacks IAM permissions to the registry
Why wrong: Permission issues would result in an authorization error, not a connection refused.
D
The build is using a public pool with no access to internal networks
Why wrong: Public pools have internet access; the error is about a private registry, likely requiring a private pool or VPC peering.

Full breakdown with real-world context →

Quick Answer

The most likely cause is that the build environment cannot reach the registry due to network restrictions. This error arises because Cloud Build’s worker pool, which runs in a Google-managed VPC, cannot establish a TCP connection to the private Docker registry located in a different project. Unlike authentication failures—which produce “denied” or “unauthorized” messages—a “connection refused” error signals that the network path is blocked, often by VPC Service Controls, firewall rules that deny egress traffic, or mismatched VPC peering configurations. On the Google Professional Cloud Developer exam, this question tests your ability to distinguish network-layer errors from credential issues, a common trap where candidates mistakenly focus on IAM permissions or service account keys. Remember the memory tip: “Refused means the door is locked, not that you lack the key.”

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 build environment cannot reach the registry due to network restrictions

The error 'connection refused' indicates a network connectivity issue, not an authentication or authorization problem. The most likely cause is that the build environment (Cloud Build) cannot reach the private Docker registry in the other project due to network restrictions such as VPC Service Controls, firewall rules, or the registry being in a different VPC network. Authentication errors would typically show 'denied' or 'unauthorized'. Therefore, option B is correct.

Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

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 registry does not exist
Why it's wrong here
If the registry doesn't exist, you'd get a name resolution or 404 error, not 'connection refused'.
✓
The build environment cannot reach the registry due to network restrictions
Why this is correct
Connection refused typically means the target is actively refusing the connection, often due to firewalls or VPC Service Controls preventing access.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The build service account lacks IAM permissions to the registry
Why it's wrong here
Permission issues would result in an authorization error, not a connection refused.
✗
The build is using a public pool with no access to internal networks
Why it's wrong here
Public pools have internet access; the error is about a private registry, likely requiring a private pool or VPC peering.

Common exam traps

Common exam trap: authentication is not authorization

Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.

Detailed technical explanation

How to think about this question

This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.

KKey Concepts to Remember

Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.

TExam Day Tips

Do not assume successful login means full administrative access.
Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
Separate login problems from permission problems before choosing the answer.

Key takeaway

Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.

Real-world example

How this comes up in practice

A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.

What to study next

Got this wrong? Here's your next step.

Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related PCD questions on access control and AAA configuration.

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FAQ

Questions learners often ask

What does this PCD question test?

Building and testing applications — This question tests Building and testing applications — Authentication checks who the user is..

What is the correct answer to this question?

The correct answer is: The build environment cannot reach the registry due to network restrictions — The error 'connection refused' indicates a network connectivity issue, not an authentication or authorization problem. The most likely cause is that the build environment (Cloud Build) cannot reach the private Docker registry in the other project due to network restrictions such as VPC Service Controls, firewall rules, or the registry being in a different VPC network. Authentication errors would typically show 'denied' or 'unauthorized'. Therefore, option B is correct.

What should I do if I get this PCD question wrong?

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?

Authentication checks who the user is.

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