Volumes in Compose in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a volume named 'data_volume' in the Compose file.

Docker

volumes:
  [1]:

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

Adata_volume

Bvolume_data

CdataVol

Dvol_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different volume name like 'volume_data' or 'dataVol'.

Misspelling the volume name.

The volume name must be exactly 'data_volume' to match the requirement.

2fill in blank

medium

Complete the service volume mount to use the volume 'data_volume' at path '/app/data'.

Docker

services:
  app:
    volumes:
      - [1]:/app/data

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

A./data_volume

Bdata_volume

C/data_volume

Dvolume_data

Attempts:

3 left

💡 Hint

Common Mistakes

Adding './' or '/' before the volume name.

Using a wrong volume name like 'volume_data'.

The volume name 'data_volume' is used directly without path prefixes.

3fill in blank

hard

Fix the error in the volume mount syntax to correctly mount 'data_volume' to '/app/data'.

Docker

services:
  app:
    volumes:
      - [1]:/app/data

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

Adata_volume-

Bdata_volume

Cdata_volume:

Ddata_volume;

Attempts:

3 left

💡 Hint

Common Mistakes

Using a space instead of a colon between volume and path.

Adding extra characters like '-' or ';' after the volume name.

The volume mount syntax requires a colon ':' between volume name and path, no spaces without colon.

4fill in blank

hard

Fill both blanks to define a named volume and mount it to '/var/lib/mysql' in the service.

Docker

volumes:
  [1]:
services:
  db:
    volumes:
      - [2]:/var/lib/mysql

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

Amysql_data

Bmysql_volume

Ddb_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for volume definition and mount.

Misspelling the volume name.

The volume name must be consistent in both definition and mount. 'mysql_data' is used for both.

5fill in blank

hard

Fill all three blanks to create a volume with driver 'local' and mount it to '/cache' in the service.

Docker

volumes:
  [1]:
    driver: [2]
services:
  cache:
    volumes:
      - [3]:/cache

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

Acache_volume

Blocal

Dcache_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using different volume names in definition and mount.

Using incorrect driver names.

The volume name 'cache_volume' is used consistently and the driver is 'local'.

Practice

1. What is the main purpose of using volumes in a Docker Compose file?

easy

A. To limit container CPU usage

B. To speed up container startup time

C. To automatically update container images

D. To keep data safe outside containers so it persists

Solution

1. Step 1: Understand volume role in Docker

   Volumes store data outside the container's writable layer, so data is not lost when containers stop or are removed.

2. Step 2: Compare options

   Options B, C, and D relate to performance or resource limits, not data persistence.

3. Final Answer:

   To keep data safe outside containers so it persists -> Option D

4. Quick Check:

   Volumes = Data persistence [OK]

Hint: Volumes = persistent data storage outside containers [OK]

Common Mistakes:

• Thinking volumes speed up container startup
• Confusing volumes with resource limits
• Assuming volumes update images automatically

2. Which of the following is the correct syntax to define a named volume in a Docker Compose file?

easy

A. services:
volumes:
- mydata:/app/data

B. volumes:
- mydata:/app/data

C. volumes:
mydata:
driver: local

D. volumes:
mydata: /app/data

Solution

1. Step 1: Identify volume declaration section

   Named volumes are declared under the top-level 'volumes:' key with a name and optional driver.

2. Step 2: Check syntax correctness

   volumes: mydata: driver: local correctly defines a named volume 'mydata' with driver 'local'. Options A, B, and D mix service and volume syntax incorrectly or have invalid mapping syntax.

3. Final Answer:

   volumes: mydata: driver: local -> Option C

4. Quick Check:

   Named volume syntax = volumes: mydata: driver: local [OK]

Hint: Define named volumes under top-level 'volumes:' with name and driver [OK]

Common Mistakes:

• Defining volumes under services instead of top-level
• Using list syntax for volume declaration
• Incorrect mapping format for volumes

3. Given this snippet in a Docker Compose file:

services:
  web:
    image: nginx
    volumes:
      - mydata:/usr/share/nginx/html
volumes:
  mydata:

What happens to the data inside /usr/share/nginx/html when the container restarts?

medium

A. Data persists because 'mydata' is a named volume

B. Data is shared with the host folder automatically

C. Data is reset to the image default every restart

D. Data is lost because volumes do not persist

Solution

1. Step 1: Understand named volume behavior

   Named volumes like 'mydata' store data outside the container and keep it between restarts.

2. Step 2: Analyze the mount point

   The volume is mounted to '/usr/share/nginx/html', so data written there is saved in 'mydata' volume.

3. Final Answer:

   Data persists because 'mydata' is a named volume -> Option A

4. Quick Check:

   Named volume mount = data persistence [OK]

Hint: Named volumes keep data safe across container restarts [OK]

Common Mistakes:

• Assuming data resets to image default
• Confusing named volumes with bind mounts
• Thinking volumes do not persist data

4. You wrote this in your Docker Compose file but get an error:

services:
  app:
    image: myapp
    volumes:
      - ./data:/app/data
volumes:
  ./data:

What is the problem?

medium

A. You cannot use relative paths under 'volumes:' top-level key

B. The image name 'myapp' is invalid

C. Bind mounts must be declared under 'volumes:' top-level key

D. The service name 'app' is reserved

Solution

1. Step 1: Understand volume declaration rules

   Top-level 'volumes:' is for named volumes only, not for bind mounts with paths.

2. Step 2: Identify misuse of relative path

   Using './data:' under 'volumes:' top-level is invalid syntax; relative paths belong only in service volume mounts.

3. Final Answer:

   You cannot use relative paths under 'volumes:' top-level key -> Option A

4. Quick Check:

   Relative paths only in service volumes [OK]

Hint: Declare bind mounts only under service volumes, not top-level [OK]

Common Mistakes:

• Putting bind mount paths under top-level volumes
• Assuming image name causes this error
• Thinking service names are restricted

5. You want to share a local folder ./config with a container's /etc/config path and also keep a database's data persistent using a named volume dbdata. Which is the correct Docker Compose snippet?

hard

A. services:
app:
image: myapp
volumes:
- dbdata:/etc/config
db:
image: postgres
volumes:
- ./config:/var/lib/postgresql/data
volumes:
dbdata:

B. services:
app:
image: myapp
volumes:
- ./config:/etc/config
db:
image: postgres
volumes:
- dbdata:/var/lib/postgresql/data
volumes:
dbdata:

C. services:
app:
image: myapp
volumes:
- /etc/config:./config
db:
image: postgres
volumes:
- /var/lib/postgresql/data:dbdata
volumes:
dbdata:

D. services:
app:
image: myapp
volumes:
- ./config:/etc/config
db:
image: postgres
volumes:
- ./dbdata:/var/lib/postgresql/data
volumes:
dbdata:

Solution

1. Step 1: Identify bind mount for local folder sharing

   Bind mounts use local paths like './config:/etc/config' under service volumes.

2. Step 2: Identify named volume for database persistence

   Named volumes like 'dbdata' are declared top-level and mounted as 'dbdata:/var/lib/postgresql/data'.

3. Step 3: Check options for correct syntax

   services: app: image: myapp volumes: - ./config:/etc/config db: image: postgres volumes: - dbdata:/var/lib/postgresql/data volumes: dbdata: correctly uses bind mount for app and named volume for db. Options B and C swap paths incorrectly. services: app: image: myapp volumes: - ./config:/etc/config db: image: postgres volumes: - ./dbdata:/var/lib/postgresql/data volumes: dbdata: uses a bind mount for dbdata instead of named volume.

4. Final Answer:

   services: app: image: myapp volumes: - ./config:/etc/config db: image: postgres volumes: - dbdata:/var/lib/postgresql/data volumes: dbdata: -> Option B

5. Quick Check:

   Bind mount + named volume = services: app: image: myapp volumes: - ./config:/etc/config db: image: postgres volumes: - dbdata:/var/lib/postgresql/data volumes: dbdata: [OK]

Hint: Use bind mounts for local folders, named volumes for persistent data [OK]

Common Mistakes:

• Swapping source and target paths
• Using bind mounts instead of named volumes for DB data
• Declaring bind mounts under top-level volumes