In applications that require persistent data storage, Docker allows managing data through volumes. Volumes ensure that data is not deleted when the container is stopped or removed, which is crucial for applications like databases. In this chapter, we will explore how to create and use volumes in Docker.

What is a Volume in Docker?

A volume is a storage unit managed by Docker that allows storing and sharing data between containers and with the host system. Volumes offer a secure and efficient way to handle persistent data.

This image shows an example of how a volume works in Docker

Creating a Volume

To create a volume, use the command docker volume create followed by the volume name:

bash

Checking Existing Volumes

To list all available volumes on the system, use the command:

bash

Mounting Volumes in Containers

Once the volume is created, it can be mounted in a container when starting it. This allows the container to access and store data in the volume.

bash

Types of Volumes

Docker offers various types of volumes to meet different storage needs:

• Anonymous Volumes: Created automatically and do not have an assigned name. They are useful for temporary storage.
• Named Volumes: Created with a specific name and are reusable in different containers.

Example of Named Volume

bash

Example of Anonymous Volume

bash

Copying Files between Container and Volume

Docker allows copying files between the host and the container's volume using the command docker cp. This is useful for transferring data without modifying the container image.

bash

Deleting Volumes

If a volume is no longer needed, it can be deleted with the command docker volume rm followed by the volume name:

bash

It is important to remember that once deleted, the data stored in the volume will be lost.

Practice: Mounting a Volume in a Web Application

Below is a practical example of how to mount a volume in a Node.js web application to store data persistently.

Example Dockerfile:

dockerfile

Command to run the container with a volume:

bash

Conclusion

Volumes are an essential tool in Docker for handling persistent data, allowing containers to store and share data securely and efficiently. In the next chapter, we will explore Docker's networking system and how containers can communicate with each other and the outside world.