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Design and plan a cloud solution architecture →easyMultiple ChoiceObjective-mapped

Google PCA Design and plan a cloud solution architecture Practice Question

This PCA practice question tests your understanding of design and plan a cloud solution architecture. 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.

Your company has migrated its legacy web application from a single Compute Engine instance to a managed instance group (MIG) behind an HTTP(S) load balancer. The application was updated to a new version as part of the migration. After the migration, users report intermittent 502 Bad Gateway errors. The application logs show no errors, and the load balancer backend health checks are reported as healthy. On investigation, the developers discover that the new version requires a specific environment variable for authentication to a downstream service. This variable was set manually on the original instance but is missing from the MIG's instance template. The health check endpoint does not depend on this variable and always returns a 200 status even when the variable is absent. As a result, instances created from the template are considered healthy by the load balancer, but when they receive requests that require authentication, they fail and return a 502 error to the client. What is the most likely cause of the 502 errors?

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.
Clue: "always"
Why it matters: Absolute qualifier. An answer using 'always' is only correct if there are genuinely no exceptions — absolute statements are often wrong in networking.

Question 1easymultiple choice

Full question →

A
The missing environment variable causes authentication failures on new instances.
The environment variable is essential for authentication; its absence causes requests to fail with 502 errors. Health checks pass because they do not exercise that code path.
B
The health check is configured to check the old application path, which no longer exists.
Why wrong: If the health check path no longer existed, the health check would fail, but it is reported as healthy, so this is not the cause.
C
The load balancer's backend timeout is too short for the application's response time.
Why wrong: A short timeout typically results in 504 Gateway Timeout errors, not 502 Bad Gateway.
D
The MIG is not scaling out fast enough to handle peak traffic.
Why wrong: Insufficient scaling would lead to 503 Service Unavailable errors or increased latency, not intermittent 502 errors from healthy instances.

Full breakdown with real-world context →

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 missing environment variable causes authentication failures on new instances.

The 502 errors occur because the new application version requires a specific environment variable for authentication to a downstream service. The health check endpoint does not depend on this variable, so instances are marked healthy even though they cannot authenticate real requests. When the load balancer routes traffic to these instances, the missing variable causes authentication failures, leading to 502 Bad Gateway errors.

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 missing environment variable causes authentication failures on new instances.
Why this is correct
The environment variable is essential for authentication; its absence causes requests to fail with 502 errors. Health checks pass because they do not exercise that code path.
Clue confirmation
The clue words "most likely", "always" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The health check is configured to check the old application path, which no longer exists.
Why it's wrong here
If the health check path no longer existed, the health check would fail, but it is reported as healthy, so this is not the cause.
✗
The load balancer's backend timeout is too short for the application's response time.
Why it's wrong here
A short timeout typically results in 504 Gateway Timeout errors, not 502 Bad Gateway.
✗
The MIG is not scaling out fast enough to handle peak traffic.
Why it's wrong here
Insufficient scaling would lead to 503 Service Unavailable errors or increased latency, not intermittent 502 errors from healthy instances.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume healthy health checks guarantee the application is fully functional, but Cisco tests the nuance that health checks may not cover all dependencies, leading to 'false healthy' instances that fail on real requests.

Detailed technical explanation

How to think about this question

The HTTP(S) load balancer uses health checks to determine instance readiness, but a health check that only verifies a basic endpoint (e.g., /health) does not validate the full application stack, including dependencies like environment variables. In this case, the health check returns 200 even when the downstream authentication fails, creating a 'false healthy' state. This is a common pitfall where health checks are not comprehensive enough to reflect actual application readiness.

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 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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this PCA question test?

Design and plan a cloud solution architecture — This question tests Design and plan a cloud solution architecture — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The missing environment variable causes authentication failures on new instances. — The 502 errors occur because the new application version requires a specific environment variable for authentication to a downstream service. The health check endpoint does not depend on this variable, so instances are marked healthy even though they cannot authenticate real requests. When the load balancer routes traffic to these instances, the missing variable causes authentication failures, leading to 502 Bad Gateway errors.

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", "always". 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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