Volumes for persistent data in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Docker volume?

A Docker volume is a special storage area managed by Docker that keeps data outside the container's writable layer. It helps data persist even if the container is deleted or recreated.

beginner

How do you create a Docker volume?

You create a Docker volume using the command: docker volume create my_volume. This makes a new volume named 'my_volume' ready to use.

beginner

How do you attach a volume to a container?

Use the docker run command with the -v option: docker run -v my_volume:/data my_image. This mounts the volume 'my_volume' inside the container at the path '/data'.

beginner

Why use volumes instead of container file system for data?

Because container file systems are temporary and deleted when the container stops. Volumes keep data safe and available even if containers are removed or updated.

beginner

How can you list all Docker volumes on your system?

Run the command docker volume ls. It shows all volumes created and available on your Docker host.

What happens to data stored inside a Docker container's file system when the container is deleted?

A The data is lost unless stored in a volume

B The data is automatically saved to the host

C The data is backed up by Docker

D The data is moved to another container

Data inside a container's file system is deleted when the container is removed. Volumes are needed to keep data persistent.

Which command creates a new Docker volume named 'data_vol'?

A docker volume create data_vol

B docker create volume data_vol

C docker volume new data_vol

D docker volume add data_vol

The correct syntax to create a volume is 'docker volume create '.

How do you mount a volume 'myvol' to '/app/data' inside a container?

A docker run -v /app/data:myvol my_image

B docker run -mount myvol:/app/data my_image

C docker run --volume /app/data:myvol my_image

D docker run -v myvol:/app/data my_image

The correct syntax is '-v volume_name:container_path'.

Which command lists all Docker volumes on your system?

A docker volume show

B docker volumes list

C docker volume ls

D docker list volumes

'docker volume ls' is the correct command to list volumes.

Why are Docker volumes preferred for storing database files?

A They encrypt data inside the container

B They keep data safe even if containers are removed

C They automatically backup data to the cloud

D They make containers run faster

Volumes keep data persistent and safe beyond the life of a container, which is important for databases.

Explain what Docker volumes are and why they are important for persistent data.

Think about what happens to data when a container is deleted.

Describe the steps and commands to create a Docker volume and use it in a container.

Focus on commands and how to connect volume to container.

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