- A
The container image is too large.
Why wrong: Image size affects cold start but not 503s under load.
- B
The Cloud Run service is hitting the maximum number of requests per second limit.
Why wrong: While possible, concurrency=1 is a more direct cause of high instance count and possible max instances limit.
- C
The API endpoint rate limits the requests.
Why wrong: External API rate limiting would cause errors from that API, not 503s from Cloud Run.
- D
Instance concurrency is too low causing request queuing and timeout.
Low concurrency forces many instances, potentially hitting max instances and causing 503s.
Question 598 of 999
PCD Deploying applications Practice Question
This PCD practice question tests your understanding of deploying 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.
A developer deploys a service on Cloud Run with a concurrency setting of 1. The service makes external API calls. Under heavy load, the service starts returning 503 errors. 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.
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
✓
Instance concurrency is too low causing request queuing and timeout.
With concurrency set to 1, each Cloud Run instance can handle only one request at a time. Under heavy load, new requests must wait for an available instance, and if the queue wait time exceeds the request timeout (default 5 minutes, max 60 minutes), the requests are dropped with a 503 HTTP status. This is the most direct cause of the 503 errors, as the service cannot scale fast enough or the queue depth exceeds limits.
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 container image is too large.
Why it's wrong here
Image size affects cold start but not 503s under load.
- ✗
The Cloud Run service is hitting the maximum number of requests per second limit.
Why it's wrong here
While possible, concurrency=1 is a more direct cause of high instance count and possible max instances limit.
- ✗
The API endpoint rate limits the requests.
Why it's wrong here
External API rate limiting would cause errors from that API, not 503s from Cloud Run.
- ✓
Instance concurrency is too low causing request queuing and timeout.
Why this is correct
Low concurrency forces many instances, potentially hitting max instances and causing 503s.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common misconception is that 503 errors are always caused by external API rate limits or downstream dependencies. However, with Google Cloud Run, a low concurrency setting can cause request queuing and timeouts, leading to 503 errors from the service itself.
Detailed technical explanation
How to think about this question
Cloud Run's concurrency setting controls how many requests a single container instance can handle simultaneously; setting it to 1 forces each instance to process requests serially. Under load, Cloud Run will attempt to scale out new instances, but scaling is limited by the container startup time and the maximum number of instances (default 100, configurable). If the request arrival rate exceeds the rate at which instances can be created and serve requests, requests queue in the Cloud Run ingress, and if the queue wait exceeds the request timeout (default 300 seconds), the ingress returns a 503. This behavior is governed by the Cloud Run request lifecycle and the 'container-runtime' timeout setting.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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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Learn the concepts, then practise the questions
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FAQ
Questions learners often ask
What does this PCD question test?
Deploying applications — This question tests Deploying applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Instance concurrency is too low causing request queuing and timeout. — With concurrency set to 1, each Cloud Run instance can handle only one request at a time. Under heavy load, new requests must wait for an available instance, and if the queue wait time exceeds the request timeout (default 5 minutes, max 60 minutes), the requests are dropped with a 503 HTTP status. This is the most direct cause of the 503 errors, as the service cannot scale fast enough or the queue depth exceeds limits.
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.
About these practice questions
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Last reviewed: Jul 4, 2026
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