Using .dockerignore - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to ignore all log files in the Docker build context.

Docker

*.[1]

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

Atxt

Blog

Cmd

Djson

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong file extension like .txt or .md

Not using the asterisk (*) wildcard before the extension

The .dockerignore file uses patterns similar to .gitignore. To ignore all log files, use *.log.

2fill in blank

medium

Complete the code to ignore the directory named 'temp' in the Docker build context.

Docker

[1]/

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

Atemp.log

Btemp.txt

Ctemp

Dtempfile

Attempts:

3 left

💡 Hint

Common Mistakes

Ignoring a file instead of a directory by adding an extension

Forgetting the trailing slash to indicate a directory

To ignore a directory, write its name followed by a slash / in the .dockerignore file.

3fill in blank

hard

Fix the error in the .dockerignore pattern to ignore all files in the 'cache' folder.

Docker

cache[1]*

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

A-

B\

C.

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using backslash instead of forward slash

Omitting the slash between directory and wildcard

To ignore all files inside the 'cache' directory, use cache/*. The slash / separates the directory name from the wildcard.

4fill in blank

hard

Fill both blanks to ignore all files with extension '.tmp' and the directory 'build' in the Docker build context.

Docker

[1]
[2]/

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

A*.tmp

Bbuild

C*.log

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing file extensions or directory names

Forgetting the slash after directory names

Use *.tmp to ignore all temporary files and build/ to ignore the build directory.

5fill in blank

hard

Fill all three blanks to ignore files named 'secret.txt', all '.env' files, and the directory 'node_modules' in the Docker build context.

Docker

[1]
[2]
[3]/

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

Asecret.txt

B*.env

Cnode_modules

Dconfig

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the slash after directory names

Using incorrect wildcards or file names

To ignore a specific file, write its name. To ignore all files with an extension, use a wildcard pattern. To ignore a directory, write its name with a trailing slash.

Practice

1. What is the main purpose of a .dockerignore file in a Docker project?

easy

A. To specify environment variables for the Docker container

B. To tell Docker which files and folders to exclude when building an image

C. To configure network settings for Docker containers

D. To list all files that must be included in the Docker image

Solution

1. Step 1: Understand the role of .dockerignore

   The .dockerignore file lists files and folders Docker should skip during image build.

2. Step 2: Compare options with this role

   Only To tell Docker which files and folders to exclude when building an image correctly states that .dockerignore excludes files/folders from the build context.

3. Final Answer:

   To tell Docker which files and folders to exclude when building an image -> Option B

4. Quick Check:

   .dockerignore excludes files from build context [OK]

Hint: Think: .dockerignore tells Docker what NOT to include [OK]

Common Mistakes:

• Confusing .dockerignore with Dockerfile
• Thinking it lists files to include instead of exclude
• Assuming it configures container runtime settings

2. Which of the following is the correct syntax to ignore the node_modules folder in a .dockerignore file?

easy

A. node_modules

B. node_modules/*

C. /node_modules/*

D. !node_modules

Solution

1. Step 1: Review .dockerignore syntax for ignoring folders

   Simply writing the folder name like node_modules ignores it and all its contents.

2. Step 2: Analyze options

   A (node_modules) is correct because it ignores the folder and its contents. B (node_modules/*) and C (/node_modules/*) ignore only contents, leaving an empty folder in the build context. D (!node_modules) negates ignoring, so it includes the folder.

3. Final Answer:

   node_modules -> Option A

4. Quick Check:

   Folder name alone ignores folder and contents [OK]

Hint: Write folder name alone to ignore it fully [OK]

Common Mistakes:

• Using ! to ignore instead of include
• Adding slashes inconsistently
• Confusing .dockerignore with .gitignore syntax

3. Given this .dockerignore content:

node_modules
secret.txt
!secret.txt.bak

Which files will be included in the Docker build context?

medium

A. secret.txt and secret.txt.bak only

B. node_modules folder, secret.txt, secret.txt.bak

C. node_modules folder and secret.txt.bak only

D. secret.txt.bak only

Solution

1. Step 1: Interpret the .dockerignore rules

   Lines exclude node_modules and secret.txt. The !secret.txt.bak line re-includes secret.txt.bak.

2. Step 2: Determine included files

   Excluded: node_modules and secret.txt. Included: secret.txt.bak because of the ! rule.

3. Final Answer:

   secret.txt.bak only -> Option D

4. Quick Check:

   ! negates ignore = include secret.txt.bak [OK]

Hint: ! before filename re-includes it despite ignore [OK]

Common Mistakes:

• Assuming ! negates all ignores
• Including ignored folders by mistake
• Ignoring the order of rules

4. You wrote this .dockerignore file:

node_modules
!node_modules/package.json

But package.json is still excluded from the build. What is the likely problem?

medium

A. Docker does not support negation (!) in .dockerignore

B. You must restart Docker daemon to apply .dockerignore changes

C. Negation does not work on files inside ignored folders

D. The syntax for negation is incorrect; use double exclamation marks (!!)

Solution

1. Step 1: Understand negation behavior in .dockerignore

   Negation (!) cannot re-include files inside a folder that is ignored entirely.

2. Step 2: Analyze the problem

   Since node_modules is ignored, negating node_modules/package.json does not include it back.

3. Final Answer:

   Negation does not work on files inside ignored folders -> Option C

4. Quick Check:

   Negation inside ignored folder fails [OK]

Hint: Negation can't rescue files inside ignored folders [OK]

Common Mistakes:

• Thinking negation always works
• Restarting Docker unnecessarily
• Using wrong negation syntax

5. You want to speed up your Docker build by excluding all .log files except important.log in the root folder. Which .dockerignore content achieves this?

hard

A. *.log
!important.log

B. *.log
!important.log
!important.log

C. *.log
!important.log
!important/*.log

D. *.log
!important.log
!important/

Solution

1. Step 1: Write rule to ignore all .log files

   Using *.log ignores all files ending with .log anywhere.

2. Step 2: Use negation to include only important.log in root

   !important.log re-includes that specific file in the root folder.

3. Final Answer:

   *.log\n!important.log -> Option A

4. Quick Check:

   Ignore all .log, then include important.log [OK]

Hint: Ignore *.log then negate important.log to include it [OK]

Common Mistakes:

• Repeating negation lines unnecessarily
• Negating folders instead of files
• Using wrong paths for negation