- A
Increase the maximum number of instances in the application tier MIG from 10 to 20.
Why wrong: Simply increasing max instances does not ensure that scaling happens quickly enough; autoscaling metrics must be tuned.
- B
Enable Cloud Armor on the frontend load balancer with a rate-limiting rule to block excessive traffic.
Why wrong: Cloud Armor is for security, not for handling legitimate traffic spikes.
- C
Configure HTTP health checks on the regional internal load balancer and set the autoscaler to use the 'HTTP load balancing utilization' metric for the application tier MIG.
Health checks ensure the load balancer only sends traffic to healthy instances, and autoscaling based on load balancing utilization will automatically adjust capacity.
- D
Enable Cloud CDN on the frontend load balancer to cache static assets and reduce load on the application tier.
Why wrong: Cloud CDN caches static content, but the 502 errors likely come from dynamic requests that are not cacheable.
Quick Answer
The correct answer is to configure HTTP health checks on the regional internal load balancer and set the autoscaler to use the 'HTTP load balancing utilization' metric for the application tier MIG. This resolves the 502 Bad Gateway errors because the frontend global load balancer returns a 502 when its backend (the nginx web servers) cannot reach a healthy application server; by autoscaling based on internal load balancer utilization, the application tier dynamically adds instances precisely when the internal load balancer detects rising traffic, preventing the backend from being overwhelmed. On the Google Professional Cloud Architect exam, this scenario tests your understanding that autoscalers can use metrics from regional internal load balancers, not just external ones—a common trap is to mistakenly scale the frontend MIG instead of the application tier. Remember the key insight: the 502 originates from the frontend, but the root cause is the application tier being saturated, so you must scale the tier behind the internal load balancer. Memory tip: "502 means the middle is weak—scale the internal tier, not the front."
Google PCA Manage implementation of cloud architecture Practice Question
This PCA practice question tests your understanding of manage implementation of cloud architecture. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A large e-commerce company runs a multi-tier application on Google Cloud. The frontend is served by a global HTTP Load Balancer with a backend service pointing to a managed instance group (MIG) of nginx web servers. The application tier consists of a regional internal TCP/UDP load balancer distributing traffic to a MIG of Java application servers. The database tier uses Cloud SQL for PostgreSQL in a failover replica configuration. The architecture is deployed in the us-central1 region across three zones. Recently, the operations team noticed intermittent 502 Bad Gateway errors from the frontend load balancer during peak traffic hours. The errors last for a few minutes and then recover. The team suspects the application tier is overwhelmed. They need to implement a solution that can handle traffic spikes without manual intervention. Which course of action should they take?
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
Configure HTTP health checks on the regional internal load balancer and set the autoscaler to use the 'HTTP load balancing utilization' metric for the application tier MIG.
Option C is correct because the intermittent 502 errors during peak traffic indicate that the application tier MIG is being overwhelmed. By configuring HTTP health checks on the regional internal load balancer and setting the autoscaler to use the 'HTTP load balancing utilization' metric, the autoscaler can scale the application tier MIG based on the actual load distribution from the internal load balancer, ensuring it handles traffic spikes without manual intervention. This directly addresses the root cause—insufficient application instances—by enabling dynamic scaling based on real-time utilization.
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.
- ✗
Increase the maximum number of instances in the application tier MIG from 10 to 20.
Why it's wrong here
Simply increasing max instances does not ensure that scaling happens quickly enough; autoscaling metrics must be tuned.
- ✗
Enable Cloud Armor on the frontend load balancer with a rate-limiting rule to block excessive traffic.
Why it's wrong here
Cloud Armor is for security, not for handling legitimate traffic spikes.
- ✓
Configure HTTP health checks on the regional internal load balancer and set the autoscaler to use the 'HTTP load balancing utilization' metric for the application tier MIG.
Why this is correct
Health checks ensure the load balancer only sends traffic to healthy instances, and autoscaling based on load balancing utilization will automatically adjust capacity.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Enable Cloud CDN on the frontend load balancer to cache static assets and reduce load on the application tier.
Why it's wrong here
Cloud CDN caches static content, but the 502 errors likely come from dynamic requests that are not cacheable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse frontend load balancer errors with frontend capacity issues and choose CDN or rate-limiting, but the 502 Bad Gateway error specifically indicates the backend (application tier) is failing to respond, so the solution must scale the application tier itself.
Detailed technical explanation
How to think about this question
The 'HTTP load balancing utilization' metric is derived from the regional internal load balancer's backend service, which tracks the ratio of current connections to the target capacity of the backend (based on max RPS or max connections). When this metric exceeds a threshold (e.g., 0.8), the autoscaler adds instances to the MIG. Under the hood, the autoscaler polls the load balancer's Stackdriver metric every 60 seconds and uses a moving average to avoid flapping. A real-world scenario where this matters is during flash sales, where traffic spikes can cause the application tier to become a bottleneck; without this metric, the autoscaler might rely on CPU utilization, which can lag behind actual request load.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
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FAQ
Questions learners often ask
What does this PCA question test?
Manage implementation of cloud architecture — This question tests Manage implementation of cloud architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure HTTP health checks on the regional internal load balancer and set the autoscaler to use the 'HTTP load balancing utilization' metric for the application tier MIG. — Option C is correct because the intermittent 502 errors during peak traffic indicate that the application tier MIG is being overwhelmed. By configuring HTTP health checks on the regional internal load balancer and setting the autoscaler to use the 'HTTP load balancing utilization' metric, the autoscaler can scale the application tier MIG based on the actual load distribution from the internal load balancer, ensuring it handles traffic spikes without manual intervention. This directly addresses the root cause—insufficient application instances—by enabling dynamic scaling based on real-time utilization.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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