【Docker】数据卷

参考教程：https://docs.docker.com/storage/volumes/
以下内容来自官方文档翻译

环境

1. virtual box 6.1
2. centos 7.8
3. docker 19.03

使用数据卷

Volumes are the preferred mechanism for persisting data generated by and used by Docker containers. While bind mounts are dependent on the directory structure and OS of the host machine, volumes are completely managed by Docker. Volumes have several advantages over bind mounts:

数据卷是持久化 Docker 容器生成和使用的数据的首选机制。因为绑定挂载依赖于主机的目录结构和操作系统，数据卷完全由 Docker 管理。和绑定挂载相比，数据卷具有几个优点：

• Volumes are easier to back up or migrate than bind mounts.
• You can manage volumes using Docker CLI commands or the Docker API.
• Volumes work on both Linux and Windows containers.
• Volumes can be more safely shared among multiple containers.
• Volume drivers let you store volumes on remote hosts or cloud providers, to encrypt the contents of volumes, or to add other functionality.
• New volumes can have their content pre-populated by a container.
• Volumes on Docker Desktop have much higher performance than bind mounts from Mac and Windows hosts.
• 数据卷比绑定挂载更容易备份或迁移。
• 您可以使用 Docker CLI 命令或 Docker API 管理数据卷。
• 数据卷同时在 Linux 和 Windows 容器上工作。
• 数据卷可以在多个容器之间更安全地共享。
• 数据卷驱动程序允许您将卷存储在远程主机或云提供商，以提供数据卷内容的加密或者其它功能。
• 新数据卷的内容可以由容器预先填充。
• 与来自 Mac 和 Windows 主机的绑定挂载相比，Docker Desktop 上的数据卷具有更高的性能。

In addition, volumes are often a better choice than persisting data in a container’s writable layer, because a volume does not increase the size of the containers using it, and the volume’s contents exist outside the lifecycle of a given container.

此外，数据卷通常比在容器的可写层中保存数据更好，因为卷不会增加使用它的容器的大小，并且卷的内容存在于给定容器的生命周期之外。

If your container generates non-persistent state data, consider using a tmpfs mount to avoid storing the data anywhere permanently, and to increase the container’s performance by avoiding writing into the container’s writable layer.

如果容器生成非持久性状态数据，请考虑使用 tmpfs 挂载以避免将数据永久存储在任何地方，并避免写入容器的可写层来提高容器的性能。

-v 和 -mount 的选择

In general, --mount is more explicit and verbose. The biggest difference is that the -v syntax combines all the options together in one field, while the --mount syntax separates them. Here is a comparison of the syntax for each flag.

一般来说，--mount 更明确和冗长。最大的区别在于， -v 语法将所有选项合并到一个字段中，而 --mount 语法将它们分开。下面是每个标志的语法的比较。

If you need to specify volume driver options, you must use --mount.

如果需要指定数据卷驱动程序选项，则必须使用 --mount。

• -v or --volume: Consists of three fields, separated by colon characters (:). The fields must be in the correct order, and the meaning of each field is not immediately obvious.

  • In the case of named volumes, the first field is the name of the volume, and is unique on a given host machine. For anonymous volumes, the first field is omitted.
  • The second field is the path where the file or directory are mounted in the container.
  • The third field is optional, and is a comma-separated list of options, such as ro. These options are discussed below.

• -v 或者 --volume：由三个字段组成，用冒号（:）分隔。字段必须按正确的顺序排列，并且每个字段的含义不是显而易见。

  • 在命名卷的情况下，第一个字段是卷的名称，在给定的主机上是唯一的。对于匿名卷，省略第一个字段。
  • 第二个字段是将文件或目录挂载到容器中的路径。
  • 第三个字段是可选的，并且是逗号分隔的选项列表，例如 ro。下面将讨论这些选项。

• --mount: Consists of multiple key-value pairs, separated by commas and each consisting of a <key>=<value> tuple. The --mount syntax is more verbose than -v or --volume, but the order of the keys is not significant, and the value of the flag is easier to understand.

• --mount：由多个键值对组成，用逗号分隔，每个键值对由 <key>=<value> 元组组成。--mount 语法比 -v 和 --volume 更详细，键的顺序不重要，并且标志的值更容易理解。

  • The type of the mount, which can be bind, volume, or tmpfs. This topic discusses volumes, so the type is always volume.

  • The source of the mount. For named volumes, this is the name of the volume. For anonymous volumes, this field is omitted. May be specified as source or src.

  • The destination takes as its value the path where the file or directory is mounted in the container. May be specified as destination, dst, or target.

  • The readonly option, if present, causes the bind mount to be mounted into the container as read-only.

  • The volume-opt option, which can be specified more than once, takes a key-value pair consisting of the option name and its value.

  • 挂载的类型，可以是 bind，volume 或者 tmpfs。本主题讨论数据卷，因此类型始终为 volume。

  • 挂载的来源。对于命名卷，这是数据卷的名称。对于匿名卷，省略此字段。可以指定为 source 或者 src

  • 挂载的目的地是文件或目录挂载在容器中的路径。可以指定为 destination， dst 或者 target。

  • 如果 readonly 存在，该选项只会挂载一个只读的数据卷。

  • volume-opt 可以指定多次，采用键值对的形式。

数据卷的操作

数据卷的所有命令

[root@master ~]# docker volume

Usage:  docker volume COMMAND

Manage volumes

Commands:
  create      Create a volume
  inspect     Display detailed information on one or more volumes
  ls          List volumes
  prune       Remove all unused local volumes
  rm          Remove one or more volumes

Run 'docker volume COMMAND --help' for more information on a command.

列出数据卷

[root@master ~]# docker volume ls --help

Usage:  docker volume ls [OPTIONS]

List volumes

Aliases:
  ls, list

Options:
  -f, --filter filter   Provide filter values (e.g. 'dangling=true')
      --format string   Pretty-print volumes using a Go template
  -q, --quiet           Only display volume names

[root@master ~]# docker volume ls
DRIVER              VOLUME NAME
local               eab77839cbab7a3123c8151031dcd2fcc71aff7a8306613502a4866d0ff232a4
local               nexus-data

创建数据卷

[root@master ~]# docker volume create --help

Usage:  docker volume create [OPTIONS] [VOLUME]

Create a volume

Options:
  -d, --driver string   Specify volume driver name (default "local")
      --label list      Set metadata for a volume
  -o, --opt map         Set driver specific options (default map[])

[root@master ~]# docker volume create my-vol
my-vol

查看数据卷

[root@master ~]# docker volume inspect --help

Usage:  docker volume inspect [OPTIONS] VOLUME [VOLUME...]

Display detailed information on one or more volumes

Options:
  -f, --format string   Format the output using the given Go template
[root@master ~]# docker volume inspect my-vol
[
    {
        "CreatedAt": "2020-10-31T06:38:43+08:00",
        "Driver": "local",
        "Labels": {},
        "Mountpoint": "/var/lib/docker/volumes/my-vol/_data",
        "Name": "my-vol",
        "Options": {},
        "Scope": "local"
    }
]
[root@master ~]#

删除数据卷

[root@master ~]# docker volume rm --help

Usage:  docker volume rm [OPTIONS] VOLUME [VOLUME...]

Remove one or more volumes. You cannot remove a volume that is in use by a container.

Aliases:
  rm, remove

Examples:

$ docker volume rm hello
hello


Options:
  -f, --force   Force the removal of one or more volumes

[root@master ~]# docker volume remove my-vol
my-vol

使用未命名数据卷

[root@master ~]# docker run -p8080:80 --mount dst=/usr/share/nginx/html -d nginx
91f5469eeeb4ffe12c385edcab40fba3b0865d366aa33b5f49010ab6cfc84cab
[root@master ~]# docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                  NAMES
91f5469eeeb4        nginx               "/docker-entrypoint.…"   9 seconds ago       Up 7 seconds        0.0.0.0:8080->80/tcp   wonderful_booth
[root@master ~]# docker volume ls
DRIVER              VOLUME NAME
local               0d34810d835e236577f6f101f0b1ebf0174973ae4a38b9d938ecf6f269a49362
local               eab77839cbab7a3123c8151031dcd2fcc71aff7a8306613502a4866d0ff232a4
local               nexus-data

[root@master ~]# docker container inspect 91 --format '{{json .Mounts}}' | jq
[
  {
    "Type": "volume",
    "Name": "0d34810d835e236577f6f101f0b1ebf0174973ae4a38b9d938ecf6f269a49362",
    "Source": "/var/lib/docker/volumes/0d34810d835e236577f6f101f0b1ebf0174973ae4a38b9d938ecf6f269a49362/_data",
    "Destination": "/usr/share/nginx/html",
    "Driver": "local",
    "Mode": "z",
    "RW": true,
    "Propagation": ""
  }
]

使用命名数据卷

[root@master ~]# docker run -P --mount src=nginx-volume,dst=/usr/share/nginx/html -d nginx
b3d9ca1cf5c1853961e004d451a289f4641d8a4af15796f85034298d3ac11ead
[root@master ~]# docker port b3d
80/tcp -> 0.0.0.0:32768
[root@master ~]#
[root@master ~]# docker volume ls
DRIVER              VOLUME NAME
local               0d34810d835e236577f6f101f0b1ebf0174973ae4a38b9d938ecf6f269a49362
local               eab77839cbab7a3123c8151031dcd2fcc71aff7a8306613502a4866d0ff232a4
local               nexus-data
local               nginx-volume
[root@master ~]# docker container inspect b3d --format '{{json .Mounts}}' | jq
[
  {
    "Type": "volume",
    "Name": "nginx-volume",
    "Source": "/var/lib/docker/volumes/nginx-volume/_data",
    "Destination": "/usr/share/nginx/html",
    "Driver": "local",
    "Mode": "z",
    "RW": true,
    "Propagation": ""
  }
]

查看数据卷详情

[root@master ~]# docker volume inspect nginx-volume
[
    {
        "CreatedAt": "2020-10-31T07:12:26+08:00",
        "Driver": "local",
        "Labels": null,
        "Mountpoint": "/var/lib/docker/volumes/nginx-volume/_data",
        "Name": "nginx-volume",
        "Options": null,
        "Scope": "local"
    }
]

只读数据卷

[root@master ~]# docker run -P --mount src=nginx-volume,dst=/usr/share/nginx/html,readonly -d nginx
7b5d9210f71f1ed7dc733b7f3151351ea41cb54b86d04f8b173fbd5f4406db7f
[root@master ~]# docker container inspect 7b5 --format '{{json .Mounts}}' | jq
[
  {
    "Type": "volume",
    "Name": "nginx-volume",
    "Source": "/var/lib/docker/volumes/nginx-volume/_data",
    "Destination": "/usr/share/nginx/html",
    "Driver": "local",
    "Mode": "z",
    "RW": false,
    "Propagation": ""
  }
]

数据卷共享数据

[root@master ~]# docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                   NAMES
7b5d9210f71f        nginx               "/docker-entrypoint.…"   4 minutes ago       Up 4 minutes        0.0.0.0:32769->80/tcp   pedantic_hugle
b3d9ca1cf5c1        nginx               "/docker-entrypoint.…"   9 minutes ago       Up 9 minutes        0.0.0.0:32768->80/tcp   boring_benz
[root@master ~]# docker exec -it b3d bash
root@b3d9ca1cf5c1:/# cd usr/share/nginx/html/
root@b3d9ca1cf5c1:/usr/share/nginx/html# ls
50x.html  index.html
root@b3d9ca1cf5c1:/usr/share/nginx/html# echo 'hello world' > index.html
root@b3d9ca1cf5c1:/usr/share/nginx/html# exit
exit
[root@master ~]# curl localhost:32769
hello world
[root@master ~]# docker volume inspect nginx-volume
[
    {
        "CreatedAt": "2020-10-31T07:12:26+08:00",
        "Driver": "local",
        "Labels": null,
        "Mountpoint": "/var/lib/docker/volumes/nginx-volume/_data",
        "Name": "nginx-volume",
        "Options": null,
        "Scope": "local"
    }
]
[root@master ~]# cat /var/lib/docker/volumes/nginx-volume/_data/index.html
hello world

数据卷的备份和恢复

生成数据卷

[root@master ~]# docker run -P -d --mount type=volume,src=nginx-volume,dst=/usr/share/nginx/html nginx:alpine
6264f7e1c20b4799845ef809fb7e065febccb25e0b75d7cfc2c32b78b76a8980
[root@master ~]# docker ps
CONTAINER ID  IMAGE                           COMMAND               CREATED         STATUS            PORTS                  NAMES
6264f7e1c20b  docker.io/library/nginx:alpine  nginx -g daemon o...  22 seconds ago  Up 5 seconds ago  0.0.0.0:44425->80/tcp  objective_johnson

修改挂载内容

[root@master ~]# docker exec -it 626 /bin/sh
/ # ls
bin                   etc                   mnt                   run                   tmp
dev                   home                  opt                   sbin                  usr
docker-entrypoint.d   lib                   proc                  srv                   var
docker-entrypoint.sh  media                 root                  sys
/ # ll
/bin/sh: ll: not found
/ # cd usr/share/nginx/html/
/usr/share/nginx/html # ll
/bin/sh: ll: not found
/usr/share/nginx/html # ls
50x.html    index.html
/usr/share/nginx/html # echo "hello world!" > index.html
/usr/share/nginx/html # exit
[root@master ~]# curl localhost:44425
hello world!

查看数据卷位置

[root@master ~]# docker volume ls
dockeDRIVER   VOLUME NAME
local    nginx-volume
[root@master ~]# docker volume inspect nginx-volume
[
     {
          "Name": "nginx-volume",
          "Driver": "local",
          "Mountpoint": "/var/lib/containers/storage/volumes/nginx-volume/_data",
          "CreatedAt": "2020-11-02T12:11:26.383688716+08:00",
          "Labels": {

          },
          "Scope": "local",
          "Options": {

          }
     }
]
[root@master ~]# cd /var/lib/containers/storage/volumes/

备份数据卷

[root@master volumes]# tar -zcvf nginx-volume.tar.gz nginx-volume
nginx-volume/
nginx-volume/_data/
nginx-volume/_data/50x.html
nginx-volume/_data/index.html
[root@master volumes]# mv nginx-volume.tar.gz ~

删除数据卷

[root@master volumes]# docker ps
CONTAINER ID  IMAGE                           COMMAND               CREATED        STATUS            PORTS                  NAMES
6264f7e1c20b  docker.io/library/nginx:alpine  nginx -g daemon o...  3 minutes ago  Up 3 minutes ago  0.0.0.0:44425->80/tcp  objective_johnson
[root@master volumes]# docker stop 626
6264f7e1c20b4799845ef809fb7e065febccb25e0b75d7cfc2c32b78b76a8980
[root@master volumes]# docker container prune
6264f7e1c20b4799845ef809fb7e065febccb25e0b75d7cfc2c32b78b76a8980
[root@master volumes]# docker volume ls
DRIVER   VOLUME NAME
local    nginx-volume
[root@master volumes]# docker volume rm nginx-volume
nginx-volume

启动新容器

[root@master volumes]# docker run -P -d --name web --mount type=volume,src=nginx-volume,dst=/usr/share/nginx/html nginx:alpine

8f5b867e5f937c84729f09031a1d44e1d1e36599ee25262775113a2e9da3c4b5
[root@master volumes]# ls
nginx-volume
[root@master volumes]# tar -zxvf ~/nginx-volume.tar.gz
nginx-volume/
nginx-volume/_data/
nginx-volume/_data/50x.html
nginx-volume/_data/index.html
[root@master volumes]# ll
total 0
drwx------. 3 root root 19 Nov  2 12:11 nginx-volume

验证还原效果

[root@master volumes]# docker ps
CONTAINER ID  IMAGE                           COMMAND               CREATED             STATUS                 PORTS                  NAMES
8f5b867e5f93  docker.io/library/nginx:alpine  nginx -g daemon o...  About a minute ago  Up About a minute ago  0.0.0.0:36962->80/tcp  web
[root@master volumes]# curl localhost:36962
hello world!

查看数据卷挂载变化

数据卷的实现方式是使用 Linux 的挂载实现的。同时，在使用 commit 创建镜像时，数据卷的内容也不会被提交。

[root@master _data]# docker container diff ed
C /var
C /var/cache
C /var/cache/nginx
A /var/cache/nginx/client_temp
A /var/cache/nginx/fastcgi_temp
A /var/cache/nginx/proxy_temp
A /var/cache/nginx/scgi_temp
A /var/cache/nginx/uwsgi_temp
C /run
A /run/nginx.pid
C /etc
C /etc/nginx
C /etc/nginx/conf.d
C /etc/nginx/conf.d/default.conf

总结

介绍了数据卷的基础使用，包括增加删除等，使用数据卷存储和共享数据，以及备份和恢复。