Multiple Compose files (override) in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to start services using the default Compose file.

Docker

docker-compose [1]

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

Aup

Bbuild

Cstart

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'build' instead of 'up' to start services

Using 'start' which only starts existing containers

Using 'run' which runs a one-off command

The docker-compose up command starts the services defined in the default docker-compose.yml file.

2fill in blank

medium

Complete the command to use an override Compose file named docker-compose.override.yml.

Docker

docker-compose -f docker-compose.yml -f [1] up

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

Adocker-compose.prod.yml

Bdocker-compose.extra.yml

Cdocker-compose.dev.yml

Ddocker-compose.override.yml

Attempts:

3 left

💡 Hint

Common Mistakes

Using a production or development file instead of the override file

Forgetting to specify the override file with -f

The -f option specifies Compose files. The override file is usually named docker-compose.override.yml.

3fill in blank

hard

Fix the error in the command to apply multiple Compose files for override.

Docker

docker-compose -f [1] -f docker-compose.override.yml up

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

Adocker-compose.override.yml

Bdocker-compose.yml

Cdocker-compose.prod.yml

Ddocker-compose.dev.yml

Attempts:

3 left

💡 Hint

Common Mistakes

Using the override file as the first file

Using a production or development file instead of the base file

The base Compose file must be docker-compose.yml before the override file.

4fill in blank

hard

Fill both blanks to override the environment variable DEBUG to true in the override file.

Docker

services:
  app:
    [2]:
      DEBUG: [1]

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

Atrue

Bfalse

Cenvironment

Dports

Attempts:

3 left

💡 Hint

Common Mistakes

Setting DEBUG to 'false' instead of 'true'

Using 'ports' instead of 'environment' key

The override file sets DEBUG to true under the environment key.

5fill in blank

hard

Fill all three blanks to correctly merge two Compose files where the override changes the image and adds a volume.

Docker

version: '3'
services:
  web:
    image: [1]
    volumes:
      - [2]
    [3]

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

Anginx:latest

B./data:/var/www/html

Cports

Dnginx:stable

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong image tag

Forgetting to add the volume mapping

Missing the ports key for exposing ports

The override changes the image to nginx:stable, adds a volume mapping, and includes the ports key for port mapping.

Practice

1. What is the main purpose of using multiple Docker Compose files with the -f option?

easy

A. To override or extend settings without changing the original compose file

B. To run multiple containers simultaneously

C. To create multiple Docker images at once

D. To speed up Docker container startup time

Solution

1. Step 1: Understand the role of multiple Compose files

   Multiple Compose files allow you to customize or override configurations without editing the original file.

2. Step 2: Recognize the use of the -f option

   The -f option lets you specify multiple files, where later files override earlier ones.

3. Final Answer:

   To override or extend settings without changing the original compose file -> Option A

4. Quick Check:

   Multiple Compose files = override settings [OK]

Hint: Multiple files with -f override earlier settings [OK]

Common Mistakes:

• Thinking multiple files run containers simultaneously
• Confusing Compose files with Docker images
• Assuming it speeds up container startup

2. Which of the following is the correct syntax to use two Docker Compose files named docker-compose.yml and docker-compose.override.yml together?

easy

A. docker-compose up -f docker-compose.yml -f docker-compose.override.yml

B. docker-compose -f docker-compose.yml -f docker-compose.override.yml up

C. docker-compose up docker-compose.yml docker-compose.override.yml

D. docker-compose -f up docker-compose.yml docker-compose.override.yml

Solution

1. Step 1: Recall the correct order of options

   The -f option must come before the command and can be repeated for multiple files.

2. Step 2: Verify the syntax correctness

   docker-compose -f docker-compose.yml -f docker-compose.override.yml up correctly places -f flags before the up command and lists both files.

3. Final Answer:

   docker-compose -f docker-compose.yml -f docker-compose.override.yml up -> Option B

4. Quick Check:

   Correct order: docker-compose -f file1 -f file2 up [OK]

Hint: Place all -f options before the command [OK]

Common Mistakes:

• Putting -f after the command
• Listing files without -f
• Mixing command and file order

3. Given these two Compose files:

docker-compose.yml:
services:
  web:
    image: nginx:1.19
    ports:
      - "80:80"

docker-compose.override.yml:
services:
  web:
    image: nginx:1.21
    environment:
      - DEBUG=true

What image version will the web service use when running docker-compose -f docker-compose.yml -f docker-compose.override.yml up?

medium

A. nginx:1.19

B. nginx:latest

C. It will cause an error due to conflicting images

D. nginx:1.21

Solution

1. Step 1: Understand override behavior

   The second file overrides matching keys from the first file, including the image version.

2. Step 2: Identify the image in the override file

   The override file sets image: nginx:1.21, which replaces nginx:1.19.

3. Final Answer:

   nginx:1.21 -> Option D

4. Quick Check:

   Override file image replaces base image [OK]

Hint: Later files override earlier image settings [OK]

Common Mistakes:

• Assuming base file image stays unchanged
• Thinking it defaults to latest
• Expecting an error from override

4. You run docker-compose -f base.yml -f override.yml up but get an error: ERROR: Service 'app' has both 'build' and 'image' specified. What is the likely cause?

medium

A. Both files define 'app' service with conflicting 'build' and 'image' keys

B. You forgot to specify the -d flag

C. The override file is missing the 'app' service definition

D. Docker Compose does not support multiple files

Solution

1. Step 1: Understand the error message

   The error says the 'app' service has both 'build' and 'image' keys, which Docker Compose disallows.

2. Step 2: Identify conflict from multiple files

   When combining files, if one file sets 'build' and another sets 'image' for the same service, this conflict occurs.

3. Final Answer:

   Both files define 'app' service with conflicting 'build' and 'image' keys -> Option A

4. Quick Check:

   Conflicting keys in combined files cause this error [OK]

Hint: Check for conflicting keys in combined service definitions [OK]

Common Mistakes:

• Thinking -d flag fixes this error
• Assuming missing service causes error
• Believing multiple files are unsupported

5. You have a base Compose file docker-compose.yml and an override docker-compose.prod.yml that changes the web service's environment variables and ports. You want to run the production setup but keep the base file unchanged. Which command correctly applies the override and ensures the web service uses the production settings?

hard

A. docker-compose up -f docker-compose.yml -f docker-compose.prod.yml -d

B. docker-compose -f docker-compose.prod.yml -f docker-compose.yml up -d

C. docker-compose -f docker-compose.yml -f docker-compose.prod.yml up -d

D. docker-compose up -d -f docker-compose.yml -f docker-compose.prod.yml

Solution

1. Step 1: Recall override order

   The last file listed with -f overrides earlier files.

2. Step 2: Check command syntax and order

   docker-compose -f docker-compose.yml -f docker-compose.prod.yml up -d correctly lists base file first, then production override, followed by the up -d command.

3. Final Answer:

   docker-compose -f docker-compose.yml -f docker-compose.prod.yml up -d -> Option C

4. Quick Check:

   Last -f file overrides earlier ones [OK]

Hint: List base file first, override file second with -f [OK]

Common Mistakes:

• Reversing file order so base overrides override
• Placing -f after the command
• Omitting -d for detached mode