What does volume mean in docker?

In docker, volume means "data volume", which can bypass the default joint file system and exist on the host in the form of a normal file or directory, thereby realizing the saving and sharing of persistent data. data between containers.

The operating environment of this tutorial: linux7.3 system, docker-1.13.1 version, Dell G3 computer.

What does volume mean in docker?

Docker Volume, usually translated as data volume, is used to save persistent data. When we run a database such as MySQL in a Docker container, we generally save the data on the host through Docker Volume. In this way, even if the MySQL container is deleted, the data is still saved on the host, effectively ensuring data security.

1. Specify Docker Volume

Use the docker run command to run a Docker container

docker run -itd --volume /tmp/data1:/tmp/data2 --name test ubuntu bash

• Created based on the ubuntu image Create a Docker container.

• The name of the container is test, specified by the –name option.

• Docker Volume is specified by the –volume option. The /tmp/data1 directory of the host corresponds to the /tmp/data2 directory in the container one-to-one.

2. View Docker Volume

Use the docker inspect command to view the detailed information of the Docker container:

docker inspect --format= '{{json .Mounts}}' test | python -m json.tool
[
{
"Destination": "/tmp/data2",
"Mode": "",
"Propagation": "",
"RW": true,
"Source": "/tmp/data1",
"Type": "bind"
}
]

• Use the –format option to selectively view the required container information. .Mount is the Docker Volume information of the container.

• python -m json.tool can format and display the output json string.

• Source represents the directory on the host, that is, /tmp/data1.

• Destination is the directory in the container, which is /tmp/data2.

3. Local files can be synchronized to the container

Create a new hello.txt file in the local/tmp/data1 directory

touch /tmp/data1/hello.txt
ls /tmp/data1/
hello.txt

hello.txt file is visible in the container/tmp/data2/ directory

Use the docker exec command to execute commands in the container.

docker exec test ls /tmp/data2/
hello.txt

It can be seen that modifications in the local directory /tmp/data1/ can be synchronized to the container directory /tmp/data2/.

4. Container files can be synchronized to the host

Create a new world.txt file in the container/tmp/data2 directory

docker exec test touch /tmp/data2/world.txt
docker exec test ls /tmp/data2/
hello.txt
world.txt

world.txt file Visible in the host/tmp/data1/ directory

ls /tmp/data1/
hello.txt world.txt

It can be seen that modifications in the container directory/tmp/data2/ can be synchronized to the host directory/tmp/data1/.

5. Conclusion

Docker Volume is essentially a directory or file shared between the container and the host, so that the data in the Docker Volume can be shared between the host and the container in real time Synchronize. When using Virtualbox to create a virtual machine, you can also configure a shared directory, which is very similar to Docker Volume.

Recommended learning: "docker video tutorial"

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