Multi-stage for different environments 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 build

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

Anode:14

Bubuntu:latest

Cpython:3.9

Dalpine:3.15

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a base image that is not suitable for building Node.js apps.

The build stage uses the Node.js 14 image as the base to compile the application.

2fill in blank

medium

Complete the Dockerfile line to copy only production dependencies in the final stage.

Docker

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

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

Anode_modules

Bpackage.json

Csrc

Ddist

Attempts:

3 left

💡 Hint

Common Mistakes

Copying source code instead of dependencies.

Copying 'node_modules' from the build stage ensures only production dependencies are included.

3fill in blank

hard

Fix the error in the Dockerfile line that sets the environment variable for production.

Docker

ENV NODE_ENV=[1]

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

Adevelopment

Btest

Cproduction

Dstaging

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'development' or 'test' instead of 'production'.

Setting NODE_ENV to 'production' ensures the app runs in production mode.

4fill in blank

hard

Fill both blanks to complete the multi-stage Dockerfile for build and production stages.

Docker

FROM [1] AS build
FROM [2] AS production

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

Anode:16

Bnode:alpine

Cpython:3.10

Dubuntu:20.04

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same image for both stages or using unrelated images.

The build stage uses the full Node 16 image, while the production stage uses a smaller Alpine image for efficiency.

5fill in blank

hard

Fill all three blanks to complete the Dockerfile snippet that copies build output and sets the command.

Docker

COPY --from=[1] /app/[2] ./
CMD ["[3]"]

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

Abuild

Bdist

Cnode

Dsrc

Attempts:

3 left

💡 Hint

Common Mistakes

Copying from wrong stage or folder, or using wrong command.

Copy from the 'build' stage the 'dist' folder and run the app using 'node' command.

Practice

1. What is the main purpose of using multi-stage builds in Docker for different environments?

easy

A. To automatically update Docker images from the internet

B. To run multiple containers simultaneously

C. To create smaller and cleaner Docker images by separating build and runtime stages

D. To increase the size of the Docker image for better performance

Solution

1. Step 1: Understand multi-stage build concept

   Multi-stage builds separate the build environment from the runtime environment to avoid including unnecessary build tools in the final image.

2. Step 2: Identify the benefit for different environments

   This separation results in smaller, cleaner images optimized for the target environment, such as production.

3. Final Answer:

   To create smaller and cleaner Docker images by separating build and runtime stages -> Option C

4. Quick Check:

   Multi-stage builds = smaller images [OK]

Hint: Remember: multi-stage means build then runtime separate [OK]

Common Mistakes:

• Thinking multi-stage runs multiple containers
• Believing it automatically updates images
• Assuming it increases image size

2. Which of the following is the correct syntax to name a build stage in a Dockerfile?

easy

A. STAGE node:18 build

B. FROM node:18 AS build

C. BUILD node:18 AS build

D. FROM node:18 WITH build

Solution

1. Step 1: Recall Dockerfile stage naming syntax

   Docker uses the syntax 'FROM <image> AS ' to name a build stage.

2. Step 2: Check each option

   Only FROM node:18 AS build uses the correct 'FROM ... AS ...' syntax; others are invalid Dockerfile commands.

3. Final Answer:

   FROM node:18 AS build -> Option B

4. Quick Check:

   Stage naming = FROM ... AS ... [OK]

Hint: Look for 'FROM ... AS ...' to name stages [OK]

Common Mistakes:

• Using 'STAGE' or 'BUILD' keywords incorrectly
• Forgetting the AS keyword
• Using 'WITH' instead of AS

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

FROM node:18 AS build
RUN npm install
FROM node:18-slim
COPY --from=build /app/node_modules /app/node_modules

medium

A. The final image will be smaller because it only copies needed files from build stage

B. The final image will be the same size as the build stage

C. The final image will fail to build due to missing files

D. The final image will be large because it includes all build tools

Solution

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

   The first stage installs dependencies with full Node image; the second stage uses a smaller Node image and copies only node_modules from the build stage.

2. Step 2: Understand image size impact

   Because only necessary files are copied, the final image is smaller than the full build environment image.

3. Final Answer:

   The final image will be smaller because it only copies needed files from build stage -> Option A

4. Quick Check:

   Copying from build stage reduces final image size [OK]

Hint: Copy only needed files from build stage to keep image small [OK]

Common Mistakes:

• Assuming all build tools are included in final image
• Thinking the build will fail due to missing files
• Believing final image equals build stage size

4. Identify the error in this Dockerfile snippet for multi-stage build:

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

medium

A. The COPY command syntax is incorrect

B. The requirements.txt file is missing

C. The base images are incompatible

D. The stage name 'builder' does not match the first stage name

Solution

1. Step 1: Check stage names consistency

   The first stage is named 'build' but COPY uses '--from=builder', which does not exist.

2. Step 2: Verify COPY command correctness

   The COPY syntax is correct, but the source stage name is wrong, causing build failure.

3. Final Answer:

   The stage name 'builder' does not match the first stage name -> Option D

4. Quick Check:

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

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

Common Mistakes:

• Using wrong stage name in COPY
• Confusing syntax errors with naming errors
• Assuming base images cause this error

5. You want to build a Docker image that uses a heavy build environment only during build, but produces a minimal runtime image for production. Which multi-stage Dockerfile snippet correctly achieves this?

hard

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

B. FROM alpine:latest AS build
RUN apk add go
WORKDIR /app
RUN go build -o app .
FROM golang:1.20
COPY --from=build /app/app /app/app
CMD ["/app/app"]

C. FROM golang:1.20
WORKDIR /app
RUN go build -o app .
CMD ["/app/app"]

D. FROM alpine:latest
RUN apk add go
WORKDIR /app
RUN go build -o app .
CMD ["/app/app"]

Solution

1. Step 1: Identify build and runtime separation

   FROM golang:1.20 AS build WORKDIR /app RUN go build -o app . FROM alpine:latest COPY --from=build /app/app /app/app CMD ["/app/app"] uses golang image for building, then copies only the built app to a minimal alpine image for runtime.

2. Step 2: Check other options for correctness

   FROM alpine:latest AS build RUN apk add go WORKDIR /app RUN go build -o app . FROM golang:1.20 COPY --from=build /app/app /app/app CMD ["/app/app"] builds in alpine but runs in golang image, which is opposite of desired minimal runtime. Options C and D do not separate build and runtime stages.

3. Final Answer:

   Option A correctly uses multi-stage build for minimal runtime image -> Option A

4. Quick Check:

   Build heavy, run minimal = FROM golang:1.20 AS build WORKDIR /app RUN go build -o app . FROM alpine:latest COPY --from=build /app/app /app/app CMD ["/app/app"] [OK]

Hint: Build in heavy image, copy to minimal runtime image [OK]

Common Mistakes:

• Building in minimal image causing slow builds
• Running heavy image in production
• Not separating build and runtime stages