Volumes for persistent data in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of the volume listing command?

You ran the command docker volume ls after creating a volume named mydata. What will the output show?

Docker

docker volume ls

A

VOLUME NAME
mydata

B

DRIVER    VOLUME NAME
local     mydata

C

local     mydata
local     otherdata

D Error: No volumes found

💡 Hint

Remember that docker volume ls shows the driver and volume name columns.

The docker volume ls command lists volumes with two columns: DRIVER and VOLUME NAME. Since you created mydata, it appears under VOLUME NAME with the driver local.

🧠 Conceptual

intermediate

Why use Docker volumes for persistent data?

Which reason best explains why Docker volumes are used for persistent data?

A Volumes allow data to persist even if the container is deleted.

B Volumes make containers run faster by using more CPU.

C Volumes automatically backup data to the cloud.

D Volumes prevent containers from using network resources.

💡 Hint

Think about what happens to data inside a container when the container is removed.

Docker volumes store data outside the container's writable layer, so data remains safe even if the container is deleted or recreated.

❓ Configuration

advanced

Which Docker Compose volume configuration mounts a host directory correctly?

Given this snippet in docker-compose.yml, which option correctly mounts the host directory /home/user/data to the container path /app/data?

Docker

services:
  app:
    image: myapp
    volumes:

A - /app/data:/home/user/data

B - /home/user/data

C - data:/app/data

D - /home/user/data:/app/data

💡 Hint

Remember the format is host_path:container_path.

In Docker Compose, to mount a host directory, you specify the host path first, then the container path separated by a colon.

❓ Troubleshoot

advanced

Why does data not persist after container restart?

You created a container with a volume, but after restarting the container, the data inside /data is missing. What is the most likely cause?

A The volume was not properly mounted to <code>/data</code> in the container.

B The host disk is full, so data cannot be saved.

C The container image deletes data on startup automatically.

D Docker volumes do not support data persistence across restarts.

💡 Hint

Check the volume mount path in the container.

If the volume is not mounted to the correct container path, data written inside the container will not be saved to the volume and will be lost on restart.

🔀 Workflow

expert

Order the steps to create and use a Docker volume for persistent data

Put these steps in the correct order to create a Docker volume and use it in a container.

A 1,3,2,4

B 2,1,3,4

C 1,2,3,4

D 3,1,2,4

💡 Hint

Think about creating the volume before using it in a container.

First, create the volume. Then run the container with the volume mounted. Next, write data inside the container to the volume path. Finally, stop and remove the container but keep the volume for data persistence.

Practice

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

easy

A. To limit container CPU usage

B. To store data persistently outside the container lifecycle

C. To speed up container startup time

D. To create network connections between containers

Solution

1. Step 1: Understand container storage

   Containers are temporary and lose data when removed unless data is stored outside.

2. Step 2: Role of volumes

   Volumes provide a way to save data persistently on the host, independent of container lifecycle.

3. Final Answer:

   To store data persistently outside the container lifecycle -> Option B

4. Quick Check:

   Persistent data = volumes [OK]

Hint: Volumes keep data safe even if container is deleted [OK]

Common Mistakes:

• Confusing volumes with container CPU limits
• Thinking volumes speed up container start
• Mixing volumes with networking features

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

easy

A. docker create volume mydata

B. docker volume new mydata

C. docker volume create mydata

D. docker volume make mydata

Solution

1. Step 1: Recall Docker volume creation command

   The correct command to create a volume is docker volume create <name>.

2. Step 2: Match syntax

   docker volume create mydata matches the correct syntax exactly.

3. Final Answer:

   docker volume create mydata -> Option C

4. Quick Check:

   Volume create command = docker volume create [OK]

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

Common Mistakes:

• Using 'create volume' instead of 'volume create'
• Using 'new' or 'make' which are invalid commands
• Mixing order of words in the command

3. Given the Docker run command:
docker run -d -v myvol:/app/data nginx
What happens to the data inside /app/data when the container is removed?

medium

A. Data remains in the named volume myvol

B. Data is deleted with the container

C. Data is copied to the host's home directory

D. Data is lost unless backed up manually

Solution

1. Step 1: Understand named volume behavior

   Named volumes like myvol store data persistently on the host.

2. Step 2: Effect of container removal

   Removing the container does not delete the named volume or its data.

3. Final Answer:

   Data remains in the named volume myvol -> Option A

4. Quick Check:

   Named volume data persists after container removal [OK]

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

Common Mistakes:

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

4. You run this command:
docker run -v /data nginx
But it fails with an error. What is the problem?

medium

A. Missing container path in volume syntax

B. Volume name /data is invalid

C. Nginx image does not support volumes

D. Docker daemon is not running

Solution

1. Step 1: Check volume syntax

   The correct volume syntax requires host_path:container_path or volume_name:container_path.

2. Step 2: Identify missing part

   Here, only one path /data is given, missing container path.

3. Final Answer:

   Missing container path in volume syntax -> Option A

4. Quick Check:

   Volume syntax needs host:container paths [OK]

Hint: Volume syntax needs two paths separated by colon [OK]

Common Mistakes:

• Using only one path in -v option
• Blaming image for volume errors
• Ignoring Docker daemon status

5. You want to share persistent data between two containers using a named volume sharedvol. Which Docker commands correctly achieve this?

hard

A. docker volume create sharedvoldocker run -v sharedvol container1docker run -v sharedvol container2

B. docker run -v sharedvol:/data container1docker run -v sharedvol:/data container2

C. docker volume create sharedvoldocker run -v /data sharedvol container1docker run -v /data sharedvol container2

D. docker volume create sharedvoldocker run -v sharedvol:/data container1docker run -v sharedvol:/data container2

Solution

1. Step 1: Create the named volume

   Use docker volume create sharedvol to make the volume first.

2. Step 2: Mount volume in both containers

   Use -v sharedvol:/data to mount the volume at /data inside each container.

3. Final Answer:

   docker volume create sharedvol
   docker run -v sharedvol:/data container1
   docker run -v sharedvol:/data container2 -> Option D

4. Quick Check:

   Named volume + mount path in both containers = sharing data [OK]

Hint: Create volume first, then mount with -v volume:path [OK]

Common Mistakes:

• Skipping volume creation step
• Reversing volume and path in -v option
• Omitting container path in volume mount