Named volumes for data sharing in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of Docker volume creation command

What is the output when you run the command to create a named volume called mydata?

Docker

docker volume create mydata

A Created volume with ID abc123

B Volume mydata created

C Error: volume name required

D mydata

💡 Hint

The command returns the volume name if successful.

The docker volume create command returns the name of the created volume, which is mydata in this case.

🧠 Conceptual

intermediate

Purpose of named volumes in Docker

Which option best describes the main purpose of using named volumes in Docker?

A To speed up container startup time by caching images

B To share data between containers and persist data beyond container life

C To isolate network traffic between containers

D To limit CPU usage of containers

💡 Hint

Think about data persistence and sharing.

Named volumes allow containers to share data and keep it even if containers are removed, unlike anonymous or bind mounts.

❓ Configuration

advanced

Correct Docker Compose volume syntax

Which Docker Compose snippet correctly defines a named volume shared_data and mounts it to /app/data inside the container?

A

volumes:
  shared_data:
services:
  app:
    volumes:
      - /app/data:shared_data

B

volumes:
  - shared_data:/app/data
volumes:
  shared_data:

C

services:
  app:
    volumes:
      - shared_data:/app/data
volumes:
  shared_data:

D

services:
  app:
    volumes:
      - /app/data:shared_data
volumes:
  shared_data:

💡 Hint

Remember the order is volume_name:container_path and volumes must be declared at root.

Option C correctly declares the named volume under volumes and mounts it inside the service under volumes with the syntax shared_data:/app/data.

❓ Troubleshoot

advanced

Troubleshooting volume data persistence issue

A developer notices that data written inside a container to a named volume is lost after the container is removed and recreated. What is the most likely cause?

A The container was started without mounting the named volume

B The volume was not declared in the Docker Compose file under <code>volumes</code>

C The volume was mounted as a bind mount to a host directory

D The container was run with <code>--rm</code> flag

💡 Hint

Check if the volume is actually connected to the container.

If the container does not mount the named volume, data is stored inside the container's writable layer and lost when the container is removed.

🔀 Workflow

expert

Order of commands to share data using named volumes

Arrange the steps in the correct order to share data between two containers using a named volume.

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 1,2,4,3

💡 Hint

You must create the volume before using it in containers.

First create the volume, then start the first container mounting it, write data, and finally start the second container mounting the same volume to share data.

Practice

1. What is the main purpose of using named volumes in Docker?

easy

A. To isolate network traffic between containers

B. To speed up container startup time

C. To share and persist data between containers safely

D. To limit CPU usage of containers

Solution

1. Step 1: Understand what named volumes do

   Named volumes store data outside the container's writable layer, allowing data to persist beyond container life.

2. Step 2: Identify the main benefit

   This persistence and sharing of data between containers is the key purpose of named volumes.

3. Final Answer:

   To share and persist data between containers safely -> Option C

4. Quick Check:

   Named volumes = data sharing and persistence [OK]

Hint: Named volumes keep data safe and share it [OK]

Common Mistakes:

• Confusing volumes with network settings
• Thinking volumes improve CPU or speed
• Assuming volumes delete data with containers

2. Which of the following is the correct command to create a named volume called mydata?

easy

A. docker volume create mydata

B. docker create volume mydata

C. docker volume new mydata

D. docker volume make mydata

Solution

1. Step 1: Recall Docker volume creation syntax

   The correct command to create a volume is docker volume create [name].

2. Step 2: Match the command with options

   Only docker volume create mydata uses the correct syntax: docker volume create mydata.

3. Final Answer:

   docker volume create mydata -> Option A

4. Quick Check:

   Volume create command = docker volume create [OK]

Hint: Use 'docker volume create' to make named volumes [OK]

Common Mistakes:

• Swapping order of words in the command
• Using 'new' or 'make' instead of 'create'
• Omitting the 'volume' keyword

3. Given the command:

docker run -d --name app1 -v myvol:/app/data busybox sleep 1000

What happens to the data inside /app/data if the container app1 is removed?

medium

A. Data inside /app/data is saved in the named volume 'myvol'

B. Data inside /app/data is lost unless backed up manually

C. Data inside /app/data is copied to the host's /var/lib/docker folder automatically

D. Data inside /app/data is deleted with the container

Solution

1. Step 1: Understand volume mounting in the command

   The -v myvol:/app/data option mounts the named volume 'myvol' to the container path '/app/data'.

2. Step 2: Know volume persistence behavior

   Named volumes keep data even if the container is removed, so data inside '/app/data' is saved in 'myvol'.

3. Final Answer:

   Data inside /app/data is saved in the named volume 'myvol' -> Option A

4. Quick Check:

   Named volume keeps data after container removal [OK]

Hint: Named volumes keep data safe after container removal [OK]

Common Mistakes:

• Thinking data deletes with container
• Confusing named volumes with anonymous volumes
• Assuming data copies to host automatically

4. You run this command to share data between two containers:

docker run -d --name c1 -v sharedvol:/data busybox sleep 1000
docker run -d --name c2 -v sharedvol:/data busybox sleep 1000

But container c2 cannot see files created by c1 inside /data. What is the likely problem?

medium

A. The volume mount syntax is incorrect

B. Containers must be on the same network to share volumes

C. The volume 'sharedvol' was not created before running containers

D. Files created by c1 are not saved because the container is stopped

Solution

1. Step 1: Check volume creation requirement

   Named volumes must exist or be created automatically. If 'sharedvol' was never created, Docker creates an empty volume.

2. Step 2: Understand volume persistence and sharing

   If 'sharedvol' was not created or data was not saved properly, c2 won't see c1's files. Network does not affect volume sharing.

3. Final Answer:

   Files created by c1 are not saved because the container is stopped -> Option D

4. Quick Check:

   Stopped container does not save files to volume [OK]

Hint: Files must be saved and container running to share data [OK]

Common Mistakes:

• Thinking network affects volume sharing
• Assuming mount syntax is wrong
• Believing stopped containers save files automatically

5. You want to share a folder /var/log/app on your host with multiple containers using a named volume. Which sequence of commands correctly creates and uses the named volume to achieve this?

hard

A. docker volume create app_logs

docker run -d -v /var/log/app:/app/log busybox sleep 1000

B. docker volume create --opt type=none --opt device=/var/log/app --opt o=bind app_logs

docker run -d -v app_logs:/app/log busybox sleep 1000

C. docker volume create app_logs

docker run -d -v app_logs:/var/log/app busybox sleep 1000

D. docker run -d -v app_logs:/app/log busybox sleep 1000

Solution

1. Step 1: Create a named volume that binds to host folder

   Use docker volume create with options type=none, device=/var/log/app, and o=bind to bind the host folder to the volume.

2. Step 2: Run container mounting the named volume

   Mount the named volume app_logs to the container path /app/log with -v app_logs:/app/log.

3. Final Answer:

   docker volume create --opt type=none --opt device=/var/log/app --opt o=bind app_logs docker run -d -v app_logs:/app/log busybox sleep 1000 -> Option B

4. Quick Check:

   Bind host folder with volume create options [OK]

Hint: Use volume create with bind options for host folder sharing [OK]

Common Mistakes:

• Mounting host folder directly without volume create
• Mounting volume to wrong container path
• Skipping volume creation step