Using Docker Volumes for Persistent Container Storage

Default Container Data Storage

We create some sample data inside a container, stop or delete the container, and observe whether the data is lost.

## 创建数据
[root@myserver ~]# docker ps
... (commands omitted for brevity) ...
# echo 12323 > tst.txt
# cat tst.txt
12323

After stopping and restarting the container, the data remains; after removing the container and recreating it, the data is lost.

Volume Usage Method

We manage Docker volumes using the docker volume command, creating a volume and mounting it into a container.

## 创建一个volume
[root@myserver ~]# docker volume create --name myvolume
myvolume
[root@myserver ~]# docker volume ls
DRIVER      VOLUME NAME
local       myvolume
[root@myserver ~]# docker volume inspect myvolume
[ { "CreatedAt": "2020-07-11T21:52:26-04:00", "Driver": "local", "Labels": {}, "Mountpoint": "/var/lib/docker/volumes/myvolume/_data", "Name": "myvolume", "Options": {}, "Scope": "local" } ]

## 在挂载点创建数据
[root@myserver ~]# cd /var/lib/docker/volumes/myvolume/_data
[root@myserver _data]# echo 11111 > a.txt
[root@myserver _data]# ls
a.txt

## 将卷挂载给容器
[root@myserver ~]# docker run -itd --name bb -v myvolume:/data:rw bulletinboard:1.0
... (container started) ...
[root@myserver ~]# docker exec -it bb bash
root@...:/data# ls
a.txt
root@...:/data# cat a.txt
11111

Alternative Volume Mounting Method

We can also specify a volume with the -v flag when starting a container; Docker will create the volume automatically if it does not exist.

# docker run -itd --name cc -v /tmp/test:/data:rw bulletinboard:1.0
... (container started) ...
# docker volume ls
DRIVER      VOLUME NAME
local       myvolume
# cd /tmp/test
# echo 111 > a.txt
# ls
a.txt
# docker exec -it cc bash
root@...:/data# ls
a.txt

Sharing Volumes Between Containers

Volumes can be shared using the --volumes-from option or by mounting the same volume in multiple containers.

# docker run -itd --name server01 -v vtest:/data webserver:v1
# docker run -itd --name server02 -v vtest:/data webserver:v1
# docker volume inspect vtest
... (inspect output) ...
# echo 123 > /var/lib/docker/volumes/vtest/_data/a.txt

# Alternative using --volumes-from
docker run -itd --name server02 --volumes-from server01 webserver:v1