The answer is that the target pool lacks health checks, causing traffic to be sent to unhealthy instances. Without explicitly configured health checks, a legacy target pool in Google Cloud will blindly distribute incoming connections from the forwarding rule to every instance in the pool, regardless of its actual state. When an instance becomes unresponsive or fails, users hitting that instance experience intermittent timeouts, while others connecting to healthy instances see normal performance. On the Google Professional Cloud Developer exam, this scenario tests your understanding of the critical difference between legacy target pools and modern backend services—a common trap is assuming health checks are automatic, when in fact they must be manually defined for target pools. Remember the mnemonic: “No check, no respect”—if you don’t configure a health check, the load balancer will not respect an instance’s health, leading to erratic failures.
PCD Practice Question: Designing highly scalable, available, and reliable cloud-native applications
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native 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.
Network Topology
You are troubleshooting a web application deployed on Compute Engine instances behind a target pool. Users report intermittent timeouts when accessing the application via the forwarding rule's IP address. Based on the exhibit, what is the most likely cause of the issue?
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 target pool lacks health checks, causing traffic to be sent to unhealthy instances.
The target pool in a legacy HTTP(S) load balancer does not automatically perform health checks unless they are explicitly configured. Without health checks, the load balancer continues to send traffic to all instances in the pool, including those that are unhealthy or unresponsive. This causes intermittent timeouts when users hit an unhealthy instance, as the forwarding rule distributes connections across the entire pool without verifying instance health.
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 forwarding rule is missing a backend service.
Why it's wrong here
Target pools do not use backend services.
✓
The target pool lacks health checks, causing traffic to be sent to unhealthy instances.
Why this is correct
Target pools rely on health checks to stop routing to unhealthy instances; without them, traffic may be routed to failed instances.
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 port range is set to 80-80, which restricts traffic to port 80 only.
Why it's wrong here
Port 80 is correct for HTTP; this would not cause timeouts.
✗
The forwarding rule should use a backend service instead of a target pool for HTTP traffic.
Why it's wrong here
Target pools can handle HTTP traffic, but health checks are still needed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a forwarding rule's port range or the use of a target pool versus a backend service is the root cause of intermittent timeouts, when in fact the absence of health checks is the critical missing component.
Detailed technical explanation
How to think about this question
In Google Cloud, a target pool is a legacy load balancing resource that distributes traffic to a group of Compute Engine instances. Health checks are defined separately and must be attached to the target pool; without them, the load balancer has no mechanism to detect instance failures. The forwarding rule simply forwards packets to the target pool, which then uses round-robin or session affinity to select an instance, regardless of its health status. This is a common pitfall when migrating from simple TCP/UDP load balancing to HTTP(S) load balancing, where health checks are mandatory for proper operation.
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.
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The target pool lacks health checks, causing traffic to be sent to unhealthy instances. — The target pool in a legacy HTTP(S) load balancer does not automatically perform health checks unless they are explicitly configured. Without health checks, the load balancer continues to send traffic to all instances in the pool, including those that are unhealthy or unresponsive. This causes intermittent timeouts when users hit an unhealthy instance, as the forwarding rule distributes connections across the entire pool without verifying instance health.
What should I do if I get this PCD 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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