Multiple FROM statements in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile to start a multi-stage build with the base image.

Docker

FROM [1]

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

Anode:14

Bubuntu:20.04

Cpython:3.9

Dalpine:latest

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a heavy image for the first stage unnecessarily increases build size.

The FROM instruction starts the build with the specified base image. Here, alpine:latest is a small, efficient base image commonly used for multi-stage builds.

2fill in blank

medium

Complete the Dockerfile to name the first build stage.

Docker

FROM alpine:latest AS [1]

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

Afinal

Bbuilder

Cbase

Druntime

Attempts:

3 left

💡 Hint

Common Mistakes

Using final for the first stage name, which is usually reserved for the last stage.

In multi-stage builds, naming the first stage builder is a common practice to indicate it is used for building the application.

3fill in blank

hard

Fix the error in the second FROM statement to use the first stage correctly.

Docker

FROM [1] AS final

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

Aalpine:latest

Bubuntu:20.04

Cbuilder

Dnode:14

Attempts:

3 left

💡 Hint

Common Mistakes

Using a base image name instead of the stage name causes build errors.

The second FROM uses the name of the first stage (builder) to copy artifacts from it. Using the stage name allows copying files without rebuilding.

4fill in blank

hard

Fill both blanks to copy the built app from the first stage and set the working directory.

Docker

COPY --from=[1] /app/build /app
WORKDIR [2]

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

Abuilder

B/app

C/usr/src/app

Dfinal

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong stage name or incorrect working directory path.

The COPY --from=builder copies files from the builder stage. Setting WORKDIR /app sets the working directory for following commands.

5fill in blank

hard

Fill all three blanks to complete the multi-stage Dockerfile that builds and runs a Node.js app.

Docker

FROM node:14 AS [1]
WORKDIR [2]
RUN npm install

FROM [3]
COPY --from=[1] [2] [2]

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

Abuilder

B/usr/src/app

Cnode:14

Dfinal

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing stage names or base images causes build or runtime errors.

The first stage is named builder and uses node:14. The working directory is set to /usr/src/app. The second stage starts from node:14 and copies files from the builder stage.

Practice

1. What is the main purpose of using multiple FROM statements in a Dockerfile?

easy

A. To create multi-stage builds that reduce final image size

B. To run multiple containers at the same time

C. To specify different base images for different containers

D. To define environment variables for the container

Solution

1. Step 1: Understand the role of FROM in Dockerfile

   The FROM statement sets the base image for building a Docker image.

2. Step 2: Recognize multi-stage build benefits

   Using multiple FROM statements allows building in stages, copying only needed files to the final image, reducing size.

3. Final Answer:

   To create multi-stage builds that reduce final image size -> Option A

4. Quick Check:

   Multiple FROM = multi-stage build [OK]

Hint: Multiple FROM means multi-stage build for smaller images [OK]

Common Mistakes:

• Thinking multiple FROM runs multiple containers
• Confusing FROM with environment variable setting
• Assuming FROM defines runtime commands

2. Which of the following is the correct syntax to copy files from a previous build stage named builder?

easy

A. COPY --stage=builder /app/build /app

B. COPY --from=builder /app/build /app

C. COPY --source=builder /app/build /app

D. COPY --stage-name=builder /app/build /app

Solution

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

   The correct flag to copy from another stage is --from=stage_name.

2. Step 2: Match the option with correct syntax

   Only COPY --from=builder /app/build /app uses --from=builder, which is valid syntax.

3. Final Answer:

   COPY --from=builder /app/build /app -> Option B

4. Quick Check:

   Copy from stage uses --from [OK]

Hint: Use COPY --from=stage_name to copy files between stages [OK]

Common Mistakes:

• Using --stage or --source instead of --from
• Misspelling the flag name
• Omitting the equals sign (=) after --from

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

FROM node:18 AS builder
RUN npm install && npm run build
FROM nginx:alpine
COPY --from=builder /app/build /usr/share/nginx/html

medium

A. Final image includes full Node.js and npm layers, making it large

B. Final image will fail to build due to missing /app/build directory

C. Final image only contains nginx and the built files, keeping it small

D. Final image contains both Node.js and nginx running simultaneously

Solution

1. Step 1: Analyze the multi-stage build steps

   The first stage builds the app with Node.js. The second stage uses nginx base image.

2. Step 2: Understand the COPY --from usage

   The built files from the builder stage are copied into nginx image, but Node.js layers are not included.

3. Final Answer:

   Final image only contains nginx and the built files, keeping it small -> Option C

4. Quick Check:

   Multi-stage copy keeps final image small [OK]

Hint: Final image excludes build tools if copied from previous stage [OK]

Common Mistakes:

• Assuming all build layers stay in final image
• Thinking COPY --from copies the entire image
• Confusing build failure with missing files

4. Identify the error in this Dockerfile snippet using multiple FROM statements:

FROM python:3.12 AS builder
RUN pip install -r requirements.txt
FROM alpine
COPY --from=build /app /app

medium

A. The stage name 'build' does not match the defined stage 'builder'

B. Alpine image cannot be used after python image

C. COPY command syntax is incorrect; missing destination path

D. pip install command should be in the second stage

Solution

1. Step 1: Check stage names in FROM statements

   The first stage is named 'builder', but COPY uses 'build' which is undefined.

2. Step 2: Understand COPY --from requires exact stage name

   Stage names must match exactly; otherwise, Docker throws an error.

3. Final Answer:

   The stage name 'build' does not match the defined stage 'builder' -> Option A

4. Quick Check:

   Stage names must match exactly in COPY --from [OK]

Hint: Match stage names exactly in COPY --from [OK]

Common Mistakes:

• Assuming similar names are accepted
• Thinking base image order matters here
• Ignoring COPY destination path correctness

5. You want to build a Docker image that compiles a Go application and then creates a minimal final image with only the compiled binary. Which Dockerfile snippet correctly uses multiple FROM statements to achieve this?

hard

A. FROM golang:1.20 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp
FROM scratch
COPY --from=builder /app/myapp /myapp
CMD ["/myapp"]

B. FROM golang:1.20
WORKDIR /app
COPY . .
RUN go build -o myapp
FROM alpine
COPY /app/myapp /myapp
CMD ["/myapp"]

C. FROM alpine AS builder
RUN apk add --no-cache go
WORKDIR /app
COPY . .
RUN go build -o myapp
FROM alpine
COPY --from=builder /app/myapp /myapp
CMD ["/myapp"]

D. FROM golang:1.20 AS builder
WORKDIR /app
COPY . .
RUN go build -o myapp
FROM alpine
COPY --from=builder /app/myapp /myapp
CMD ["/myapp"]

Solution

1. Step 1: Identify the build stage with Go compiler

   Stage named 'builder' uses golang image to compile the app.

2. Step 2: Use a minimal runtime image for final stage

   The final stage uses alpine (small image) and copies only the binary from builder.

3. Step 3: Verify COPY --from syntax and CMD

   COPY uses --from=builder to get binary; CMD runs the binary correctly.

4. Final Answer:

   FROM golang:1.20 AS builder WORKDIR /app COPY . . RUN go build -o myapp FROM alpine COPY --from=builder /app/myapp /myapp CMD ["/myapp"] -> Option D

5. Quick Check:

   Multi-stage build with builder and minimal final image [OK]

Hint: Use builder stage for compile, minimal image for final [OK]

Common Mistakes:

• Using scratch without proper setup
• Copying files without --from flag
• Building in final stage instead of builder