The answer is to remove the global mutex and ensure request handling is asynchronous. This is correct because a global mutex forces sequential processing on a single-threaded Node.js event loop, blocking all other requests until the current one finishes—directly causing the high latency under load. By removing the mutex and using async/await or Promises, the event loop can interleave I/O-bound tasks, allowing concurrent request handling without changing infrastructure. On the Google Professional Cloud Developer exam, this scenario tests your understanding of Cloud Run’s stateless, concurrent request model and Node.js’s non-blocking I/O; a common trap is assuming you need more CPU or instances, when the real fix is code-level concurrency. Remember the mnemonic: “No lock, no block—async unlocks the clock.”
PCD Building and testing applications Practice Question
This PCD practice question tests your understanding of building and testing applications. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 Cloud Run service experiences high latency under load. The service is a Node.js Express app that processes requests sequentially due to a global mutex. What is the most effective solution?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the mutex and ensure request handling is asynchronous
The root cause is that the global mutex forces sequential processing, negating Node.js's asynchronous event loop. Removing the mutex and ensuring asynchronous request handling (e.g., using async/await or Promises) allows the single-threaded event loop to interleave I/O-bound tasks, dramatically reducing latency under concurrent load. This directly addresses the bottleneck without changing the underlying infrastructure.
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.
✓
Remove the mutex and ensure request handling is asynchronous
Why this is correct
This directly addresses the bottleneck by allowing parallel processing.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Cloud Run for Anthos to handle load
Why it's wrong here
Moving to Anthos does not fix the concurrency issue within the application.
✗
Increase the number of CPUs per container
Why it's wrong here
More CPUs won't help if requests are blocked by a mutex.
✗
Increase the 'max-instances' setting
Why it's wrong here
More instances still have the mutex per instance, so latency may persist.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that scaling infrastructure (more CPUs, more instances) can fix application-level concurrency bugs, when the real solution is to fix the code to be non-blocking.
Detailed technical explanation
How to think about this question
Node.js uses an event-driven, non-blocking I/O model where a single thread handles all requests via the event loop. A global mutex (e.g., a synchronous lock or a blocking operation) stalls the event loop, preventing it from processing other requests until the mutex is released. In practice, this often occurs when using synchronous file system calls (fs.readFileSync) or a poorly designed critical section; replacing these with asynchronous equivalents (fs.promises.readFile) allows the event loop to continue handling other requests while waiting for I/O.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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.
Building and testing applications — This question tests Building and testing applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Remove the mutex and ensure request handling is asynchronous — The root cause is that the global mutex forces sequential processing, negating Node.js's asynchronous event loop. Removing the mutex and ensuring asynchronous request handling (e.g., using async/await or Promises) allows the single-threaded event loop to interleave I/O-bound tasks, dramatically reducing latency under concurrent load. This directly addresses the bottleneck without changing the underlying infrastructure.
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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Question Discussion
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