Multi-stage builds for static sites in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of multi-stage Docker build for static site

Given this Dockerfile for a static site using multi-stage build, what will be the output of docker images after building?

Nginx

FROM node:18 AS builder
WORKDIR /app
COPY . .
RUN npm install && npm run build

FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html

A An image named 'node' with the source code and node_modules installed

B An image named 'nginx' with the static site files in /usr/share/nginx/html

C Two images: one for 'node' builder and one for 'nginx' with static files

D No images created because multi-stage builds do not produce images

💡 Hint

Think about what the final stage in a multi-stage build produces as the image.

Multi-stage builds produce only the final stage as the image. The builder stage is temporary and not saved as an image unless tagged separately.

❓ Configuration

intermediate

Correct COPY command in multi-stage Dockerfile

Which COPY command correctly copies the built static files from the builder stage to the nginx image in a multi-stage Dockerfile?

A COPY --from=nginx /app/dist /usr/share/nginx/html

B COPY /app/dist /usr/share/nginx/html

C COPY --from=builder /app/dist /usr/share/nginx/html

D COPY --from=builder /usr/share/nginx/html /app/dist

💡 Hint

Remember to specify the source stage and correct source and destination paths.

The correct syntax is COPY --from=builder . The source is the build output directory in the builder stage.

🔀 Workflow

advanced

Order of steps in multi-stage Dockerfile for static site

Arrange the following steps in the correct order for a multi-stage Dockerfile that builds a static site and serves it with nginx.

A 4,1,2,3

B 4,2,1,3

C 2,4,1,3

D 1,4,2,3

💡 Hint

Start with the builder stage, then build, then switch to nginx stage and copy files.

First define the builder stage (4), run build commands (1), then define nginx stage (2), and finally copy built files (3).

❓ Troubleshoot

advanced

Why does nginx serve a 404 error after multi-stage build?

You built a static site with a multi-stage Dockerfile but nginx returns 404 for all pages. What is the most likely cause?

A The COPY command copied files to the wrong directory inside nginx image

B The builder stage failed to run npm install

C nginx image does not support static files

D The Dockerfile is missing the EXPOSE 80 instruction

💡 Hint

Check where nginx expects static files to be located.

nginx serves files from /usr/share/nginx/html by default. If files are copied elsewhere, nginx returns 404.

✅ Best Practice

expert

Optimizing multi-stage Dockerfile for smallest image size

Which practice best reduces the final image size when building a static site with multi-stage Dockerfile?

A Run npm install in the final stage instead of builder stage

B Install all build tools in the final nginx image

C Copy node_modules folder to the final image for caching

D Use a minimal base image like nginx:alpine for the final stage

💡 Hint

Think about what is needed in the final image to serve static files only.

Using a minimal base image like nginx:alpine keeps the final image small by excluding build tools and unnecessary files.

Practice

1. What is the main benefit of using multi-stage builds for static sites with nginx?

easy

A. It automatically updates static files without rebuilding the image.

B. It allows running multiple nginx servers in one container.

C. It reduces the final image size by separating build and serve stages.

D. It enables dynamic content generation inside the nginx container.

Solution

1. Step 1: Understand multi-stage build purpose

   Multi-stage builds separate the build process from the final image, so only necessary files are included.

2. Step 2: Identify benefits for static sites

   This separation reduces the final image size and improves security by excluding build tools from the runtime image.

3. Final Answer:

   It reduces the final image size by separating build and serve stages. -> Option C

4. Quick Check:

   Multi-stage builds = smaller images [OK]

Hint: Remember: build tools stay out of final image for smaller size [OK]

Common Mistakes:

• Thinking multi-stage runs multiple nginx servers
• Believing static files update automatically without rebuild
• Confusing static site builds with dynamic content generation

2. Which Dockerfile snippet correctly copies static files from a builder stage to the nginx stage?

easy

A. COPY --to=builder /app/dist /usr/share/nginx/html

B. COPY /app/dist /usr/share/nginx/html --from=builder

C. COPY /usr/share/nginx/html /app/dist --from=builder

D. COPY --from=builder /app/dist /usr/share/nginx/html

Solution

1. Step 1: Recall correct COPY syntax for multi-stage

   The syntax is COPY --from=stage source_path destination_path.

2. Step 2: Match snippet to syntax

   COPY --from=builder /app/dist /usr/share/nginx/html uses COPY --from=builder /app/dist /usr/share/nginx/html which is correct.

3. Final Answer:

   COPY --from=builder /app/dist /usr/share/nginx/html -> Option D

4. Quick Check:

   COPY --from=stage source dest = correct [OK]

Hint: COPY uses --from=stage before source path [OK]

Common Mistakes:

• Placing --from after paths
• Using --to instead of --from
• Reversing source and destination paths

3. Given this Dockerfile snippet, what will be the size impact on the final image?

FROM node:18 AS builder
WORKDIR /app
COPY . .
RUN npm run build

FROM nginx:alpine
COPY --from=builder /app/dist /usr/share/nginx/html

medium

A. Final image will be small because only nginx and static files are included.

B. Final image will be empty because build files are not copied.

C. Final image will be large because node is included.

D. Final image will contain both node and nginx layers.

Solution

1. Step 1: Analyze multi-stage build layers

   The builder stage uses node to build files, but the final stage uses nginx:alpine only.

2. Step 2: Understand what is copied to final image

   Only the /app/dist folder from builder is copied into nginx image, so node and build tools are excluded.

3. Final Answer:

   Final image will be small because only nginx and static files are included. -> Option A

4. Quick Check:

   Multi-stage excludes build tools = smaller image [OK]

Hint: Final image excludes builder tools, so size stays small [OK]

Common Mistakes:

• Assuming node stays in final image
• Thinking build files are missing
• Believing both node and nginx layers combine

4. You wrote this Dockerfile but the static files are missing in the nginx container:

FROM node:18 AS builder
WORKDIR /app
COPY . .
RUN npm run build

FROM nginx:alpine
COPY /app/dist /usr/share/nginx/html

What is the error?

medium

A. COPY command misses --from=builder to copy from the build stage.

B. npm run build did not generate files in /app/dist.

C. nginx:alpine image does not support static files.

D. WORKDIR is not set in the nginx stage.

Solution

1. Step 1: Check COPY command in final stage

   The COPY command lacks --from=builder, so it copies from the current stage which is empty.

2. Step 2: Understand multi-stage copy syntax

   To copy files from builder stage, COPY must use --from=builder to access that stage's files.

3. Final Answer:

   COPY command misses --from=builder to copy from the build stage. -> Option A

4. Quick Check:

   Missing --from=builder causes empty copy [OK]

Hint: Always use --from=builder to copy from build stage [OK]

Common Mistakes:

• Forgetting --from=builder in COPY
• Assuming build files auto-copy without --from
• Blaming nginx image for missing files

5. You want to optimize your multi-stage Dockerfile for a static site by minimizing layers and image size. Which approach is best?

hard

A. Combine build and nginx in one stage to avoid copying files.

B. Use a builder stage to create static files, then copy only those files into a minimal nginx image.

C. Install node and build tools inside the nginx image to keep one image.

D. Copy the entire project folder into nginx image to ensure all files are present.

Solution

1. Step 1: Understand multi-stage build best practices

   Best practice is to separate build tools from runtime to keep images small and secure.

2. Step 2: Choose approach minimizing layers and size

   Using a builder stage to create static files, then copying only those files into a minimal nginx image achieves this.

3. Final Answer:

   Use a builder stage to create static files, then copy only those files into a minimal nginx image. -> Option B

4. Quick Check:

   Separate build and serve stages = optimized image [OK]

Hint: Build separately, copy only static files to nginx [OK]

Common Mistakes:

• Combining build and serve increases image size
• Installing build tools in nginx image adds unnecessary layers
• Copying entire project wastes space and layers