Multi-stage builds for static sites in Nginx - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a multi-stage build in Docker?

A multi-stage build is a Docker technique that uses multiple FROM statements in one Dockerfile to create smaller, optimized images by separating build and runtime environments.

beginner

Why use multi-stage builds for static sites?

Multi-stage builds help keep the final image small by only including the static files needed to serve the site, removing build tools and dependencies.

intermediate

In a multi-stage build for a static site, what is typically done in the first stage?

The first stage usually installs dependencies and builds the static site files using tools like npm or yarn.

beginner

What role does nginx play in multi-stage builds for static sites?

Nginx serves the static files in the final stage, providing a lightweight and fast web server environment.

intermediate

How does a multi-stage Dockerfile improve security for static sites?

By excluding build tools and source code from the final image, it reduces the attack surface and potential vulnerabilities.

What is the main benefit of using multi-stage builds for static sites?

A Smaller final image size

B Faster build times

C More layers in the image

D Includes all build tools in the final image

Multi-stage builds reduce the final image size by only copying necessary files to the last stage.

Which tool is commonly used to serve static sites in the final stage of a multi-stage build?

A Apache

B Node.js

C Nginx

D MySQL

Nginx is a lightweight web server often used to serve static files efficiently.

In a multi-stage Dockerfile, what does the first stage usually contain?

A Final runtime environment

B Static files only

C Nginx configuration

D Build tools and source code

The first stage installs dependencies and builds the static site.

How does multi-stage building affect security?

A Increases attack surface

B Reduces vulnerabilities by excluding build tools

C Includes all source code in the final image

D Requires more permissions

Excluding build tools and source code reduces the attack surface.

Which Dockerfile instruction is used to copy files from one stage to another?

A COPY --from

B RUN

C ADD

D ENV

COPY --from allows copying files from a previous build stage.

Explain how a multi-stage Docker build works for creating a static site with nginx.

Think about separating build and runtime environments.

Describe the advantages of using multi-stage builds for static sites in terms of performance and security.

Consider what is included and excluded in the final image.

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