The answer is to enable container concurrency and set max instances to a high value. Container concurrency allows a single Cloud Run instance to handle multiple simultaneous requests—up to 1,000—which dramatically boosts throughput during traffic spikes without needing to spin up new containers. Setting max instances high ensures the service can scale out aggressively, creating enough parallel instances to absorb sudden load and prevent request queuing or cold starts. On the Google Professional Cloud Developer exam, this tests your understanding of Cloud Run’s dual scaling dimensions: vertical (concurrency per instance) and horizontal (instance count). A common trap is thinking only one dimension matters—candidates often max instances but forget concurrency, or vice versa. Remember the mnemonic “Concurrency for density, Max for capacity” to recall that concurrency packs requests into fewer containers, while max instances gives you the ceiling to burst outward.
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. 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 company is using Cloud Run for a stateless API. They want to ensure that the service can handle sudden traffic spikes. Which two features should they configure?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable container concurrency.
Option A is correct because enabling container concurrency allows a single Cloud Run container instance to handle multiple requests simultaneously, up to the configured concurrency limit (default 80, max 1000). This improves throughput and resource utilization during traffic spikes without requiring additional instances. Option D is correct because setting max instances to a high value ensures the service can scale out to handle sudden load by creating more container instances, up to the configured maximum, preventing cold starts and request queuing.
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.
✓
Enable container concurrency.
Why this is correct
Container concurrency allows multiple requests per container, increasing throughput.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Cloud Load Balancing.
Why it's wrong here
Cloud Run already distributes traffic; an external LB is not needed for a single service.
✗
Enable CPU always on allocation.
Why it's wrong here
CPU always on is for background processing, not scaling.
✓
Set max instances to a high value.
Why this is correct
High max instances allows scaling out to handle more requests.
Related concept
Read the scenario before looking for a memorised answer.
✗
Set min instances to zero to save cost.
Why it's wrong here
Zero min instances causes cold starts during spikes.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that Cloud Load Balancing is required for scaling Cloud Run, but Cloud Run's built-in autoscaling and managed HTTPSload balancer already handle traffic spikes; the trap is that candidates confuse external load balancing with internal scaling mechanisms.
Detailed technical explanation
How to think about this question
Under the hood, Cloud Run uses Knative serving, where container concurrency is implemented via the `containerConcurrency` field in the Knative Service spec, controlling how many requests are routed to a single container instance. Setting max instances to a high value (e.g., 1000) allows the Knative autoscaler to create more pods (instances) based on concurrency metrics, but note that Cloud Run has a soft limit of 1000 instances per region per project, and exceeding this requires a quota increase. In a real-world scenario, a service with concurrency set to 80 and max instances set to 1000 can handle up to 80,000 concurrent requests, but if max instances is left at the default (100), the service would be limited to 8,000 concurrent requests, potentially causing 429 errors during spikes.
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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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: Enable container concurrency. — Option A is correct because enabling container concurrency allows a single Cloud Run container instance to handle multiple requests simultaneously, up to the configured concurrency limit (default 80, max 1000). This improves throughput and resource utilization during traffic spikes without requiring additional instances. Option D is correct because setting max instances to a high value ensures the service can scale out to handle sudden load by creating more container instances, up to the configured maximum, preventing cold starts and request queuing.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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