The data volume is the fundamental building block of data sharing in the Docker environment. Before getting into the details of data sharing, it is imperative to gain a good understanding of the Data Volume concept. Until now, all the files that we created in an image or a container are part and parcel of the Union filesystem. However, the data volume is part of the Docker host filesystem, and it simply gets mounted inside the container.

A data volume can be inscribed in a Docker image using the VOLUME instruction of the Dockerfile. Also, it can be prescribed during the launch of a container using the -v option of the docker run subcommand. Here, in the following example, the implication of the VOLUME instruction in the Dockerfile is illustrated in detail, in the following steps: