Today I Learned: About Docker Volume

In my experiements on running Jenkins on Docker, I wondered how the volumne worked when I provided -v to the run command.

I found a great article which succintly explains a lot about the Docker Volume - which will be handy for any docker beginer.

Original article is here

My summary goes below:

• Docker Volume is the way to persist data between container restarts and share it between containers.
• A volume is stored on the host file system. Usually within obscure directories inside /var/lib/docker. However, a specific directory on host system can also be mounted as volume in a container.
• Volumes can be managed using docker volume and its sub commands.
• Docker won't delete volume unless specifically instructed to do so. This can result in stale data on the host system. So tidying up once in a while might come handy.
• Important Caveat - Don't try to modify the content of the volume in the Dockerfile (via RUN) as each build step creates a new volume and your changes will be discarded. If you want to change the volume content, do so using the ENTRYPOINT command in the Dockerfile. Have a look at this link.
• If you are looking for a thorough overview of different approaches to manage application data, including the use of Volume, Bind mounts, tmpfs mounts, read this longer article

Image Credit: https://docs.docker.com/engine/admin/volumes/images/types-of-mounts-volume.png