The correct choice is to use a multi-stage Dockerfile with a distroless base image. This approach works because multi-stage builds let you compile dependencies and install tools in a heavy build stage, then copy only the compiled application and its runtime essentials into a final, minimal stage. By switching to a distroless image like gcr.io/distroless/nodejs, you strip away shells, package managers, and unnecessary OS utilities, leaving just your Node.js app and its core runtime. On the Google Professional Cloud Developer exam, this question tests your understanding of container optimization for Cloud Run, where image size directly impacts cold start latency and security posture. A common trap is choosing a single-stage build with a full OS image like Ubuntu, which bloats the container and increases the attack surface. Remember the memory tip: “Build big, run small—distroless drops the shell.”
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 developer wants to containerize a Node.js application and deploy it to Cloud Run. They need to ensure the container is as small as possible. What should they do?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a multi-stage Dockerfile with a distroless base image.
Option B is correct because a multi-stage Dockerfile allows you to separate the build environment from the runtime environment. By using a distroless base image (e.g., gcr.io/distroless/nodejs), you include only the application and its runtime dependencies, omitting package managers, shells, and other OS utilities. This results in a significantly smaller container image, which reduces attack surface and improves deployment speed on Cloud Run.
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.
✗
Use a full Ubuntu base image with all dependencies.
Why it's wrong here
Results in large image size.
✓
Use a multi-stage Dockerfile with a distroless base image.
Why this is correct
Multi-stage builds copy only runtime dependencies, and distroless images are minimal.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a node:latest image and remove unnecessary files.
Why it's wrong here
Still includes many tools not needed at runtime.
✗
Use a simple FROM scratch image.
Why it's wrong here
Scratch has no libraries; Node.js requires a base OS.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that 'FROM scratch' is the smallest possible image for any application, but candidates must recognize that scratch images lack the runtime libraries required by interpreted languages like Node.js, making distroless the correct minimal choice.
Detailed technical explanation
How to think about this question
Multi-stage builds work by using multiple FROM statements in a single Dockerfile; the first stage (e.g., node:18) installs dependencies and compiles the application, while the final stage copies only the built artifacts into a minimal base image like distroless. Distroless images are based on Debian but stripped of package managers, shells, and other non-essential binaries, reducing the image to roughly 20–30 MB for Node.js. In a real-world scenario, this matters for Cloud Run because smaller images cold-start faster (often under 1 second) and reduce egress costs, while also minimizing the blast radius of a container breakout vulnerability.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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: Use a multi-stage Dockerfile with a distroless base image. — Option B is correct because a multi-stage Dockerfile allows you to separate the build environment from the runtime environment. By using a distroless base image (e.g., gcr.io/distroless/nodejs), you include only the application and its runtime dependencies, omitting package managers, shells, and other OS utilities. This results in a significantly smaller container image, which reduces attack surface and improves deployment speed on Cloud Run.
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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