Docker - Storage & Volumes

Each docker container has its own isolated volume. By default, this volume isn't persistent, meaning that if the container restarts or gets deleted, then so does its data.

To have persistent data on a container, you have to map a directory on the docker host, to a directory on the container.

docker run -v /path/on/host:/path/on/container containername

Example;

I have a MySQL container that I need to keep persistent data on. To do this, I would map the /var/lib/mysql directory on the container, to a location on the docker host.

docker run -v /opt/mysql_container_data:/var/lib/mysql mysql

There are 2 methods that can be used to create a docker volume;

Using docker run -v without creating a volume beforehand:

You can directly specify a volume using the -v flag during docker run without pre-creating the volume. Docker will automatically create a volume if it doesn't find one matching your specification.

You can create a volume manually using docker volume create before running the container:

This is useful if you want to manage the volume lifecycle explicitly (naming, inspecting, and configuring it before use).When you manually create a volume, you can inspect it, set specific options, and organize your persistent storage more systematically.

To mount a pre-existing data volume to a docker container, you would still use the -v flag:
```
docker run -v volume_name:/path/on/container containername
```