volume container 是專門為其他容器提供 volume 的容器，他提供的卷也可以是bind mount ，也可以是docker managed volume
建立容器vc_data，因為它只負責提供資料，無需執行，docker create即可。
容器mount了兩個volume，bind mount用來存放webserver的靜態檔案，docker managed volume用來存放一些實用工具
[root@docker-lab ~]# cat ~/htdocs/index.html
This a test HTML file
[root@docker-lab ~]# docker create --name vc_data -v ~/htdocs:/usr/local/apache2/htdocs -v /other/useful/tools busybox
6c12ead74cd754c2da6e0e801b798a93d38965d84fc2eea9c120bcf627e99560
[root@docker-lab ~]# docker inspect vc_data
"Mounts": [
{
"Type": "bind",
"Source": "/root/htdocs",
"Destination": "/usr/local/apache2/htdocs",
"Mode": "",
"RW": true,
"Propagation": "rprivate"
},
{
"Type": "volume",
"Name": "14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696",
"Source": "/var/lib/docker/volumes/14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696/_data",
"Destination": "/other/useful/tools",
"Driver": "local",
"Mode": "",
"RW": true,
"Propagation": ""
}
]
其他容器可以使用 --volumes-from 使用vc_data 這個volume container
[root@docker-lab ~]# docker run --name web01 -d -p 80 --volumes-from vc_data httpd
90feafa492fe582ba97072e660a5661587b14bd40de60d6b78d14a3127294328
[root@docker-lab ~]# docker run --name web02 -d -p 80 --volumes-from vc_data httpd
a04615d5f438bc609ce35e04c2a3d76bb6df78e627d4136cf56e83b18d794517
[root@docker-lab ~]# docker run --name web03 -d -p 80 --volumes-from vc_data httpd
88613c4f0e6cd112a359bf68dfe515e7469883ea76f2df85f37c022f84e5fd63
[root@docker-lab ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
88613c4f0e6c httpd "httpd-foreground" 3 seconds ago Up 2 seconds 0.0.0.0:32770->80/tcp web03
a04615d5f438 httpd "httpd-foreground" 8 seconds ago Up 7 seconds 0.0.0.0:32769->80/tcp web02
90feafa492fe httpd "httpd-foreground" 13 seconds ago Up 12 seconds 0.0.0.0:32768->80/tcp web01
[root@docker-lab ~]# docker inspect web01 -f '{{.NetworkSettings.IPAddress}}'
172.17.0.2
[root@docker-lab ~]# docker inspect web02 -f '{{.NetworkSettings.IPAddress}}'
172.17.0.3
[root@docker-lab ~]# docker inspect web03 -f '{{.NetworkSettings.IPAddress}}'
172.17.0.4
[root@docker-lab ~]# curl http://127.0.0.1:32768
This a test HTML file
[root@docker-lab ~]# curl http://127.0.0.1:32769
This a test HTML file
[root@docker-lab ~]# curl http://127.0.0.1:32770
This a test HTML file
[root@docker-lab ~]# docker inspect vc_data -f '{{.Mounts}}'
[
{bind /root/htdocs /usr/local/apache2/htdocs true rprivate}
{volume 14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696 /var/lib/docker/volumes/14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696/_data /other/useful/tools local true }
]
[root@docker-lab ~]# docker inspect web01 -f '{{.Mounts}}'
[
{bind /root/htdocs /usr/local/apache2/htdocs true rprivate}
{volume 14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696 /var/lib/docker/volumes/14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696/_data /other/useful/tools local true }
]
[root@docker-lab ~]# docker inspect web02 -f '{{.Mounts}}'
[
{bind /root/htdocs /usr/local/apache2/htdocs true rprivate}
{volume 14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696 /var/lib/docker/volumes/14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696/_data /other/useful/tools local true }
]
[root@docker-lab ~]# docker inspect web03 -f '{{.Mounts}}'
[
{bind /root/htdocs /usr/local/apache2/htdocs true rprivate}
{volume 14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696 /var/lib/docker/volumes/14ae5efb5762a333bcceb26503ca974122d67cf31ed68da1b22773065b6fa696/_data /other/useful/tools local true }
]
上面可以看到三個web容器都成功的共享了 volume container 中的volume。
volume container 特點：
1、與bind mount 相比，不必為每一個容器指定host path，所有path都在volume container的容器中定義，容器只需要與volume container關聯，實現了容器與host的解耦
2、使用volume container 的容器其mount point是一致的，有利於配置和的規範和標準化，也帶來一定的侷限性，使用時需要綜合考慮