The answer is Cloud Build triggers with filepath filters, combined with a build script that uses git diff to detect changes. This approach works because filepath filters allow you to trigger builds only when specific directories or files are modified, while a custom build script can compare the current commit hash against the last successful build’s commit hash, using git diff to identify exactly which modules changed and then conditionally execute build steps for only those modules. On the Google Professional Cloud Developer exam, this tests your understanding of optimizing CI/CD pipelines for monorepos, often appearing as a scenario where you must avoid rebuilding unchanged modules to save time and cost. A common trap is assuming Cloud Build’s built-in caching alone handles this, but caching only reuses artifacts, not skips builds entirely. Memory tip: think “trigger filter + diff script” as the two-part key to module-level selective builds.
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 company has a multi-module repository. They want to build only the modules that have changes. Which two features can they combine to achieve this? (Choose 2)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Build scripts that detect changes
Option B is correct because build scripts can be written to compare the current commit hash against the previous build's commit hash, or use git diff to detect which files have changed, and then conditionally execute build steps only for the affected modules. This approach gives fine-grained control over the build process and can be integrated into any CI/CD pipeline.
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.
✗
Cloud Build queue
Why it's wrong here
Queue manages build ordering, not filtering.
✓
Build scripts that detect changes
Why this is correct
A build step can run a script (e.g., `git diff`) to identify changed modules and conditionally execute subsequent steps.
Related concept
Read the scenario before looking for a memorised answer.
✗
Cloud Build substitutions
Why it's wrong here
Substitutions are variable placeholders, not used for conditional building based on changed files.
✓
Cloud Build triggers with filepath filters
Why this is correct
Filepath filters can trigger builds only when changes occur in specific directories, avoiding unnecessary builds.
Related concept
Read the scenario before looking for a memorised answer.
✗
Cloud Source Repositories mirror
Why it's wrong here
Mirroring is for syncing external repositories, not for building only changed modules.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between features that trigger builds (like triggers with filepath filters) and features that manage build execution or configuration (like substitutions or queues), leading candidates to mistakenly select options that sound related but do not actually detect changes.
Detailed technical explanation
How to think about this question
Under the hood, build scripts can leverage `git diff --name-only HEAD~1 HEAD` to list changed files, then parse the output to determine which modules need rebuilding. This approach is often combined with caching strategies to avoid rebuilding unchanged modules, and it works well in monorepo setups where each module has its own build context. A real-world scenario is a large microservices monorepo where only the changed service and its dependencies are rebuilt, dramatically reducing build times.
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: Build scripts that detect changes — Option B is correct because build scripts can be written to compare the current commit hash against the previous build's commit hash, or use git diff to detect which files have changed, and then conditionally execute build steps only for the affected modules. This approach gives fine-grained control over the build process and can be integrated into any CI/CD pipeline.
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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