Docker volumes are used to keep data persistent when the container is
restarted or deleted. By default, if the container stops or deletes, all
data from the docker is lost.
Assume a mongo database is configured and running on a docker. We have
stored a variety of data in the database, but the container of the mongo
database has been stopped or removed.
We will be unable to find any data in the database the next time we build
or restart the mongo container. And this could result in significant data
loss, which would have to be migrated if it was possible.
So Docker volumes come into play to avoid such a catastrophe and make
data persistent.
Three different types of Docker volumes exist.
1. Host volumes: This is where the data stored in host machine
directly.
2. Anonymous volumes: These are volumes where data is saved in a random
directory established by Docker.
3. Named volumes: This is where data is kept in a random directory
defined by Docker but with a unique name. This is quite useful, and with
the tags attached, it is also very easy to manage.
The -v parameter can be used with the docker run command to define the
docker volume.
/data/db is the directory on the container where data is kept for mongo db, and
mongo-data is the name of the volume.
And docker generates a directory in the host computer according to the
name of the volume, for example inside docker/volumes.
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