Docker is a popular open-source containerization platform that allows users to package and deploy applications in lightweight containers. These containers are isolated from each other and provide a consistent environment for running applications, regardless of the host operating system.
One of the key features of Docker is the ability to use volumes to persist data generated by and used by Docker containers. In this article, we will explore what Docker volumes are, how they work, and how to use them with an example.
What is a Docker volume?
A Docker volume is a persistent storage location for data that is accessed by Docker containers. This data is stored outside the containers and is not deleted when the container is removed. This allows you to persist data generated by and used by your containers, even if the container itself is deleted.
Volumes are useful for a variety of purposes, including storing database data, configuration files, and other data that needs to be persisted outside the container.
How do Docker volumes work?
When you run a Docker container, you can use the
--volume flag to specify a volume that should be mounted into the container. This flag takes the following format:
-v /host/path:/container/path This tells Docker to mount the host path /host/path into the container at /container/path. This means that anything written to the /container/path location inside the container will be written to the /host/path location on the host machine.
In addition to mounting host paths, you can also use Docker volumes, which are managed by Docker itself. To create a Docker volume, you can use the docker volume create command, like this:
docker volume create my-volume This will create a new Docker volume named my-volume. You can then mount this volume into a container using the -v or --volume flag, like this:
docker run -v my-volume:/container/path my-image This will mount the my-volume volume into the container at the /container/path location. Any data written to this location inside the container will be stored in the my-volume volume and will be persisted even if the container is deleted.
Example: Using a Docker volume with a database
One common use case for Docker volumes is storing the data for a database. For example, suppose you want to run a MySQL database inside a Docker container. You could use a Docker volume to persist the data for the database, even if the container is deleted.
To do this, you would first create a Docker volume to store the database data:
docker volume create db-data Next, you would run the MySQL container and mount the db-data volume into it, like this:
docker run -v db-data:/var/lib/mysql mysql This will run the MySQL container and mount the
db-data volume at the
/var/lib/mysql location inside the container. This is the default location where MySQL stores its data, so any data written to this location inside the container will be written to the
db-data volume on the host machine.
Even if the MySQL container is deleted, the data in the
db-data volume will be persisted, and you can use it with a new MySQL container by simply mounting the volume into the new container.
Docker volumes are a powerful and useful tool for managing data in Docker containers. They allow you to persist data generated by and used by your containers, even if the containers themselves are deleted. Volumes can be used to store a wide variety of data, including database data, configuration files, and more. By using Docker volumes, you can ensure that your data is persisted and easily accessible, even as you deploy and update your containers.