The answer is Cloud Build triggers with filepath filters. This feature allows you to define included files and ignored files patterns so that a trigger only fires when a commit modifies code within specific directories, making it the ideal solution for selectively building changed services in a monorepo. On the Google Professional Cloud Developer exam, this question tests your understanding of how to optimize CI/CD pipelines for monorepo architectures without triggering unnecessary builds across all services. A common trap is confusing filepath filters with branch filters, which only scope triggers to specific Git branches rather than file paths. Remember the memory tip: "Branch filters control *when* you build; filepath filters control *what* you build."
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 monorepo with multiple services. They want to only build and test the services that have changed in a given commit. Which Cloud Build feature should they use?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Build triggers with filepath filters
Cloud Build triggers support filepath filters (also called 'included files' and 'ignored files'), which allow the trigger to fire only when changes occur in specific paths. This is ideal for monorepos. Branch filters are for branches, not files. Substitutions are variables, not filtering. Custom builders don't provide this logic.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Build triggers with filepath filters
Why this is correct
Filepath filters (included_files/ignored_files) limit the trigger to specific paths, enabling per-service builds.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use a custom builder image
Why it's wrong here
Custom builders don't provide per-path filtering; the trigger configuration does.
✗
Build triggers with branch filters
Why it's wrong here
Branch filters only filter by branch name, not by which files changed.
✗
Use Cloud Build substitutions
Why it's wrong here
Substitutions are variables that allow parameterization, they do not filter which builds run.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. 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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCD NAT questions on configuration and troubleshooting.
Building and testing applications — This question tests Building and testing applications — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Build triggers with filepath filters — Cloud Build triggers support filepath filters (also called 'included files' and 'ignored files'), which allow the trigger to fire only when changes occur in specific paths. This is ideal for monorepos. Branch filters are for branches, not files. Substitutions are variables, not filtering. Custom builders don't provide this logic.
What should I do if I get this PCD question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCD NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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