Builder pattern before multi-stage in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile line to specify the base image for the build stage.

Docker

FROM [1] AS builder

Drag options to blanks, or click blank then click option'

Anode:18-alpine

Bubuntu:latest

Cpython:3.12-slim

Dalpine:3.18

Attempts:

3 left

💡 Hint

Common Mistakes

Using a base image without Node.js when building a Node app.

Choosing a heavy image like full Ubuntu unnecessarily.

The node:18-alpine image is a lightweight Node.js base image commonly used for building Node.js apps.

2fill in blank

medium

Complete the command to copy package.json and package-lock.json into the builder stage.

Docker

COPY [1] ./

Drag options to blanks, or click blank then click option'

Adist/

Bpackage*.json

Cnode_modules/

Dsrc/

Attempts:

3 left

💡 Hint

Common Mistakes

Copying the entire source folder instead of just package files.

Copying node_modules folder which should be built inside the container.

Using package*.json copies both package.json and package-lock.json files needed for installing dependencies.

3fill in blank

hard

Fix the error in the RUN command to install dependencies in the builder stage.

Docker

RUN npm [1]

Drag options to blanks, or click blank then click option'

Astart

Bbuild

Cinstall

Dtest

Attempts:

3 left

💡 Hint

Common Mistakes

Using npm start which runs the app instead of installing.

Using npm build which is not a valid npm command.

The npm install command installs all dependencies listed in package.json.

4fill in blank

hard

Fill both blanks to copy built files from the builder stage to the final image.

Docker

COPY --from=[1] [2] ./app/

Drag options to blanks, or click blank then click option'

Abuilder

B/app/dist

C/dist

Dfinal

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong stage name in --from.

Copying from a wrong or non-existent folder.

The --from=builder copies files from the builder stage, and /dist is the typical output folder for built files.

5fill in blank

hard

Fill all three blanks to define the final image base, set working directory, and expose port.

Docker

FROM [1]
WORKDIR [2]
EXPOSE [3]

Drag options to blanks, or click blank then click option'

Anode:18-alpine

B/app

C3000

Dubuntu:latest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a heavy base image for final stage.

Forgetting to set working directory.

Exposing wrong or no port.

The final image uses node:18-alpine as base, sets /app as working directory, and exposes port 3000 for the app.

Practice

1. What is the main purpose of the builder pattern in Docker before multi-stage builds were introduced?

easy

A. To run multiple containers simultaneously

B. To separate the build environment from the final runtime environment

C. To automatically update Docker images

D. To manage Docker volumes efficiently

Solution

1. Step 1: Understand the builder pattern concept

   The builder pattern splits the process into two parts: building the app and running it.

2. Step 2: Identify the benefit of separation

   This separation keeps the final image small by excluding build tools and files.

3. Final Answer:

   To separate the build environment from the final runtime environment -> Option B

4. Quick Check:

   Builder pattern = separate build and run [OK]

Hint: Builder pattern means build and run are separate stages [OK]

Common Mistakes:

• Confusing builder pattern with running multiple containers
• Thinking it manages volumes or updates automatically
• Assuming it is about Docker networking

2. Which Dockerfile snippet correctly implements the builder pattern before multi-stage builds?

easy

A. FROM node:14
WORKDIR /app
COPY . .
RUN npm install && npm run build
CMD ["npm", "start"]

B. FROM node:14 AS builder
WORKDIR /app
COPY . .
RUN npm install && npm run build
FROM nginx:alpine
COPY --from=builder /app/build /usr/share/nginx/html

C. FROM node:14
RUN npm install
COPY . .
CMD ["npm", "start"]

D. FROM nginx:alpine
COPY . /usr/share/nginx/html
RUN npm install

Solution

1. Step 1: Identify builder pattern before multi-stage

   Before multi-stage, builder pattern used separate Dockerfiles or manual copying, not the --from syntax.

2. Step 2: Check each option

   FROM node:14 AS builder WORKDIR /app COPY . . RUN npm install && npm run build FROM nginx:alpine COPY --from=builder /app/build /usr/share/nginx/html uses multi-stage syntax (--from=builder), which was not available before multi-stage builds.

3. Final Answer:

   FROM node:14 WORKDIR /app COPY . . RUN npm install && npm run build CMD ["npm", "start"] -> Option A

4. Quick Check:

   Before multi-stage, no --from usage [OK]

Hint: Before multi-stage, no --from in COPY command [OK]

Common Mistakes:

• Choosing multi-stage syntax before it existed
• Confusing build and runtime commands
• Ignoring the CMD instruction

3. Given this Dockerfile before multi-stage builds:

FROM node:14
WORKDIR /app
COPY . .
RUN npm install && npm run build
CMD ["node", "server.js"]

What is the likely size impact on the final image?

medium

A. The image will be large because build tools and source files remain

B. The image will be small because only build output is copied

C. The image size is minimal due to automatic cleanup

D. The image size depends only on the base image

Solution

1. Step 1: Analyze the Dockerfile steps

   The Dockerfile copies all source files and runs build inside the same image.

2. Step 2: Understand image size impact

   Since build tools and source files remain, the image size is larger than needed.

3. Final Answer:

   The image will be large because build tools and source files remain -> Option A

4. Quick Check:

   Single-stage build keeps all files, so image is large [OK]

Hint: Single-stage build keeps all files, making image large [OK]

Common Mistakes:

• Assuming build output only is copied
• Thinking Docker cleans up build files automatically
• Ignoring the COPY . . step

4. You have two Dockerfiles: one for building and one for running. You want to copy build artifacts from the builder image to the runtime build context manually. Which command correctly copies files from a stopped builder container named 'builder' to the runtime build context?

medium

A. docker cp ./build builder:/app/build

B. docker copy builder:/app/build ./build

C. docker cp builder:/app/build ./build

D. docker copy ./build builder:/app/build

Solution

1. Step 1: Understand docker cp syntax

   The correct syntax is 'docker cp <container>:<source_path> <destination_path>'.

2. Step 2: Match command to copy from container to local

   docker cp builder:/app/build ./build correctly copies from container 'builder' path to local './build'.

3. Final Answer:

   docker cp builder:/app/build ./build -> Option C

4. Quick Check:

   docker cp container:path local_path [OK]

Hint: Use 'docker cp container:path local_path' to copy files out [OK]

Common Mistakes:

• Using 'docker copy' instead of 'docker cp'
• Reversing source and destination paths
• Trying to copy from local to container incorrectly

5. You want to manually implement the builder pattern before multi-stage builds by using two Dockerfiles: Dockerfile.build and Dockerfile.run. Which sequence of commands correctly builds and prepares the final image with only the build output copied?

hard

A. docker build -f Dockerfile.build -t app-builder . && docker run --name builder app-builder && docker cp builder:/app/dist ./dist && docker rm builder && docker build -f Dockerfile.run -t app-runtime .

B. docker build -f Dockerfile.run -t app-runtime . && docker build -f Dockerfile.build -t app-builder .

C. docker build -f Dockerfile.run -t app-runtime . && docker run --name builder app-builder && docker cp builder:/app/dist ./dist

D. docker build -f Dockerfile.build -t app-builder . && docker create --name builder app-builder && docker cp builder:/app/dist ./dist && docker rm builder && docker build -f Dockerfile.run -t app-runtime .

Solution

1. Step 1: Build the builder image and create a container

   Use 'docker build' with Dockerfile.build, then 'docker create' to make a stopped container for copying files.

2. Step 2: Copy build output and build runtime image

   Copy files from the builder container, remove it, then build the runtime image with Dockerfile.run.

3. Final Answer:

   docker build -f Dockerfile.build -t app-builder . && docker create --name builder app-builder && docker cp builder:/app/dist ./dist && docker rm builder && docker build -f Dockerfile.run -t app-runtime . -> Option D

4. Quick Check:

   Build, create, copy, remove, then build runtime [OK]

Hint: Create container to copy files, then build runtime image [OK]

Common Mistakes:

• Using 'docker run' instead of 'docker create' for copying
• Building runtime image before copying build output
• Not removing temporary builder container