Image size and minimal base images in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile to use a minimal base image for a Python app.

Docker

FROM [1]
COPY app.py /app.py
CMD ["python", "/app.py"]

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

Anode:latest

Bubuntu:latest

Cdebian:latest

Dpython:3.12-slim

Attempts:

3 left

💡 Hint

Common Mistakes

Using a full OS image like ubuntu increases image size unnecessarily.

Choosing an unrelated base image like node for a Python app.

The python:3.12-slim image is a minimal base image optimized for Python apps, reducing image size.

2fill in blank

medium

Complete the Dockerfile to reduce image size by removing cache after package installation.

Docker

FROM alpine:3.18
RUN apk add --no-cache [1]
CMD ["sh"]

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

Apython3 --cache

Bpython3

Cpython3 --no-cache

Dpython3-cache

Attempts:

3 left

💡 Hint

Common Mistakes

Adding cache flags as part of the package name causes errors.

Not using --no-cache leads to larger images.

The --no-cache flag in apk add prevents caching of the package index, reducing image size.

3fill in blank

hard

Fix the error in the Dockerfile to use a minimal base image for a Node.js app.

Docker

FROM [1]
COPY server.js /server.js
CMD ["node", "/server.js"]

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

Anode:alpine

Bnode:latest

Cnode:slim

Dubuntu

Attempts:

3 left

💡 Hint

Common Mistakes

Using node:latest results in a larger image.

Using ubuntu is not optimized for Node.js apps.

The node:alpine image is a minimal base image for Node.js, reducing image size compared to node:latest.

4fill in blank

hard

Fill both blanks to create a Python Dockerfile that uses a minimal base image and installs packages without cache.

Docker

FROM [1]
RUN apk add --no-cache [2]
CMD ["python3"]

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

Apython:3.12-alpine

Bpython3

C--no-cache

Dpython3-pip

Attempts:

3 left

💡 Hint

Common Mistakes

Using a full Python image increases size.

Not using --no-cache causes larger images.

Use python:3.12-alpine for a minimal Python base image and --no-cache with apk add to avoid cache files.

5fill in blank

hard

Fill all three blanks to create a minimal Dockerfile that copies app files, installs dependencies without cache, and runs the app.

Docker

FROM [1]
COPY [2] /app/
RUN pip install [3] -r /app/requirements.txt
COPY app.py /app/
CMD ["python3", "/app/app.py"]

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

Apython:3.12-alpine

Bapp.py

C--no-cache-dir

Drequirements.txt

Attempts:

3 left

💡 Hint

Common Mistakes

Copying the app.py instead of requirements.txt before installing dependencies.

Not using --no-cache-dir increases image size.

Use python:3.12-alpine for a small base image, copy requirements.txt to install dependencies, and use --no-cache-dir to avoid cache files.

Practice

1. Which base image is known for being very small and commonly used to create minimal Docker images?

easy

A. Ubuntu

B. Alpine

C. Debian

D. CentOS

Solution

1. Step 1: Understand common base images

   Ubuntu, Debian, and CentOS are full Linux distributions and tend to be larger in size.

2. Step 2: Identify minimal base images

   Alpine is a lightweight Linux distribution designed for minimal size, often under 10 MB.

3. Final Answer:

   Alpine -> Option B

4. Quick Check:

   Minimal base image = Alpine [OK]

Hint: Alpine is the go-to small base image for minimal Docker images [OK]

Common Mistakes:

• Choosing Ubuntu or Debian as minimal base images
• Confusing full distributions with minimal ones
• Not knowing Alpine is designed for small size

2. Which of the following Dockerfile base image declarations is syntactically correct for using Alpine Linux?

easy

A. FROM alpine:latest

B. BASE alpine

C. USE alpine

D. IMAGE alpine

Solution

1. Step 1: Recall Dockerfile syntax for base images

   The correct keyword to specify a base image is FROM followed by the image name and optional tag.

2. Step 2: Check each option

   Only 'FROM alpine:latest' uses the correct syntax. Others are invalid Dockerfile commands.

3. Final Answer:

   FROM alpine:latest -> Option A

4. Quick Check:

   Base image syntax = FROM [OK]

Hint: Base images start with FROM in Dockerfiles [OK]

Common Mistakes:

• Using incorrect keywords like BASE or USE
• Omitting the FROM keyword
• Not specifying image tag correctly

3. Given this Dockerfile snippet:

FROM alpine:3.18
RUN apk add --no-cache curl

What is the main reason this image remains small compared to using Ubuntu as base?

medium

A. Alpine automatically removes all packages after installation

B. Alpine installs curl faster than Ubuntu

C. Ubuntu images do not support curl installation

D. Alpine uses apk with --no-cache to avoid cache files, reducing size

Solution

1. Step 1: Understand Alpine's package manager behavior

   Alpine uses apk, and the --no-cache option prevents storing temporary cache files, keeping the image small.

2. Step 2: Compare with Ubuntu

   Ubuntu uses apt which caches package files unless explicitly cleaned, increasing image size.

3. Final Answer:

   Alpine uses apk with --no-cache to avoid cache files, reducing size -> Option D

4. Quick Check:

   apk --no-cache reduces image size [OK]

Hint: Use apk add --no-cache on Alpine to keep images small [OK]

Common Mistakes:

• Thinking Alpine installs packages faster
• Believing Ubuntu can't install curl
• Assuming Alpine removes all packages automatically

4. You wrote this Dockerfile:

FROM alpine
RUN apk add curl

But your final image is much larger than expected. What is the likely cause?

medium

A. You forgot to use --no-cache with apk add, so cache files remain

B. Alpine base image is always large regardless of commands

C. You should use Ubuntu base image for smaller size

D. The RUN command syntax is incorrect

Solution

1. Step 1: Analyze apk add command

   Without --no-cache, apk stores cache files in the image, increasing size.

2. Step 2: Understand base image size and syntax

   Alpine is small by default, RUN syntax is correct, and Ubuntu is larger, so those are not causes.

3. Final Answer:

   You forgot to use --no-cache with apk add, so cache files remain -> Option A

4. Quick Check:

   Missing --no-cache causes larger images [OK]

Hint: Always add --no-cache with apk to keep Alpine images small [OK]

Common Mistakes:

• Assuming Alpine is large by default
• Using wrong RUN syntax
• Switching to Ubuntu thinking it is smaller

5. You want to create the smallest possible Docker image for a Go application. Which base image and approach is best to minimize image size?

hard

A. Use FROM ubuntu and install Go runtime

B. Use FROM alpine and install full Go toolchain

C. Use FROM scratch and copy only the compiled Go binary

D. Use FROM debian and add all dependencies

Solution

1. Step 1: Understand the scratch base image

   Scratch is an empty image with zero size, ideal for copying only necessary files like a compiled binary.

2. Step 2: Compare other options

   Ubuntu, Alpine, and Debian add extra layers and packages, increasing image size unnecessarily.

3. Final Answer:

   Use FROM scratch and copy only the compiled Go binary -> Option C

4. Quick Check:

   Scratch + compiled binary = smallest image [OK]

Hint: Use scratch base and copy binary for tiniest Go images [OK]

Common Mistakes:

• Installing full runtimes increasing image size
• Using larger base images unnecessarily
• Not using multi-stage builds to compile separately