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Building and testing applications →mediumMultiple ChoiceObjective-mapped

Fix 'Module not found' on App Engine Flexible by Installing Dependencies in Build

This PCD practice question tests your understanding of building and testing 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 team uses Cloud Build to build and deploy a Node.js application to App Engine flexible environment. The build succeeds, but the deployment fails with 'ERROR: (gcloud.app.deploy) Error Response: [9] Application startup error!' The team checks logs and sees 'Error: Module not found: 'express''. 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.

Quick Answer

The answer is that the dependencies are not installed during the build step before deploying. This is the most likely cause because in the App Engine flexible environment, the build process in Cloud Build compiles your code, but the runtime container only includes what you explicitly install—if you do not run `npm install` (or your package manager’s equivalent) as part of the build steps, the required modules like 'express' will be missing when the application starts, triggering the "Module not found" error. On the Google Professional Cloud Developer exam, this scenario tests your understanding of the separation between build and runtime phases in Cloud Build for App Engine flexible; a common trap is assuming that the build’s success implies all dependencies are present, but the build only packages your source code unless you explicitly install them. Remember the memory tip: "Build compiles, install supplies"—always ensure your Cloud Build configuration includes a step to install dependencies before the deploy step.

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

✓

The dependencies are not installed during the build step before deploying.

Option D is correct because the error 'Module not found: express' indicates that the Node.js dependencies (specifically the 'express' package) are not present in the deployed application. In Cloud Build, the build steps must explicitly install dependencies (e.g., via 'npm install') before the deploy step. If the build configuration does not include an 'npm install' step, the dependencies listed in package.json are not copied to the App Engine flexible environment, causing the startup error.

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 build step includes 'npm test' which fails.

    Why it's wrong here

    If test fails, build fails, not deployment startup.

  • ✗

    The Node.js version specified in app.yaml is incompatible with the dependencies.

    Why it's wrong here

    Version mismatch usually gives engine error, not module not found.

  • ✗

    The app.yaml file is missing from the root of the repository.

    Why it's wrong here

    Missing app.yaml would cause a different error earlier.

  • ✓

    The dependencies are not installed during the build step before deploying.

    Why this is correct

    Dependencies must be installed (e.g., npm install) for the app to run.

    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

Google often tests the distinction between build-time and deployment-time errors, and the trap here is that candidates might confuse a missing app.yaml (a configuration error) with a missing dependency (a runtime error), or assume that npm install is automatically performed by Cloud Build when it is not.

Detailed technical explanation

How to think about this question

Under the hood, App Engine flexible environment uses a Docker container to run the application. The build step in Cloud Build must generate the application artifacts, including the node_modules directory. If 'npm install' is not executed during the build, the node_modules folder is absent from the deployed image, leading to the 'Module not found' error. A common real-world scenario is when a team uses a pre-built image or forgets to include the install step in the cloudbuild.yaml file, assuming dependencies are bundled elsewhere.

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.

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FAQ

Questions learners often ask

What does this PCD question test?

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: The dependencies are not installed during the build step before deploying. — Option D is correct because the error 'Module not found: express' indicates that the Node.js dependencies (specifically the 'express' package) are not present in the deployed application. In Cloud Build, the build steps must explicitly install dependencies (e.g., via 'npm install') before the deploy step. If the build configuration does not include an 'npm install' step, the dependencies listed in package.json are not copied to the App Engine flexible environment, causing the startup error.

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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Last reviewed: Jul 4, 2026

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This PCD practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCD exam.