6.Docker容器数据卷

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1. 什么是容器数据卷

先来看看Docker的理念:

  • 将应用与运行的环境打包形成容器运行 ，运行可以伴随着容器，但是我们对数据的要求希望是持久化的
  • 容器之间希望有可能共享数据

Docker容器产生的数据，如果不通过docker commit生成新的镜像，使得数据做为镜像的一部分保存下来，那么当容器删除后，数据自然也就没有了。为了能保存数据在docker中我们使用卷。

2. 容器数据卷能做什么

  1. 容器数据的持久化
  2. 容器之间继承和共享数据

3. 添加数据卷的方式

3.1 直接使用命令添加

  • 语法:

docker run -it -v /宿主机目录:/容器内目录 centos /bin/bash

–privileged=true: 防止出现Permission denied

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[root@localhost software]# docker run -it -d -p 9995:8080 -v /usr/local/software/tomcat_p_9995/:/usr/local/tomcat/webapps --privileged=true tomcat:8.5
1f53c5b786b9a57843e5fa714afb7d7b8151614b5c2f602029c14d1a229a417a
[root@localhost software]# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS              PORTS                    NAMES
1f53c5b786b9        tomcat:8.5          "catalina.sh run"   About a minute ago   Up About a minute   0.0.0.0:9995->8080/tcp   hardcore_volhard
[root@localhost software]#
  • 查看容器卷是否挂载成功

"Source", "Destination"

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[root@localhost docs]# docker inspect 1f53c5b786b9
[
    {
        "Id": "1f53c5b786b9a57843e5fa714afb7d7b8151614b5c2f602029c14d1a229a417a",
        ...
        "Mounts": [
            {
                "Type": "bind",
                "Source": "/usr/local/software/tomcat_p_9995",
                "Destination": "/usr/local/tomcat/webapps",
                "Mode": "",
                "RW": true,
                "Propagation": "rprivate"
            }
        ]
        ...
    }
]

3.2 使用DockerFile添加

1.创建文件夹docker

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# mkdir docker

2.在文件夹docker中创建名为Dockerfile的文件

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# vim Dockerfile

3.编写Dockerfile的文件

VOLUME ["/usr/local/tomcat/webapps"]是容器内的路径

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#基于tomcat:8.5构造一个镜像
FROM tomcat:8.5
#加入容器卷
VOLUME ["/usr/local/tomcat/webapps"]
CMD echo "finished,--------success1"
CMD /bin/bash

4.使用Dockerfile生成自定义镜像

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[root@localhost docker]# docker build -t mytomcat01:1.0 .

output:

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Sending build context to Docker daemon 2.048 kB
Step 1/4 : FROM tomcat:8.5
 ---> 0eed806285b5
Step 2/4 : VOLUME /usr/local/tomcat/webapps
 ---> Running in e9e49a42c671
 ---> cb2c0e6605ec
Removing intermediate container e9e49a42c671
Step 3/4 : CMD echo "finished,--------success1"
 ---> Running in eba00d668afc
 ---> fb505e1a2e79
Removing intermediate container eba00d668afc
Step 4/4 : CMD /bin/bash
 ---> Running in 773a1ba24d77
 ---> b14e2098d46d
Removing intermediate container 773a1ba24d77
Successfully built b14e2098d46d

查看生成的镜像

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[root@localhost docker]# docker images
REPOSITORY              TAG                 IMAGE ID            CREATED             SIZE
mytomcat01              1.0                 b14e2098d46d        4 seconds ago       533 MB
docker.io/tomcat        8.5                 0eed806285b5        11 days ago         533 MB
docker.io/nginx         latest              f35646e83998        4 weeks ago         133 MB
docker.io/hello-world   latest              bf756fb1ae65        10 months ago       13.3 kB

5.使用docker inspect 容器ID查看容器卷

运行一个docker实例

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# docker run -it -d -p 9991:8080 mytomcat01:1.0 /bin/bash
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# docker inspect 1ea64d3c6cfa

output:

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...
        "Mounts": [
            {
                "Type": "volume",
                "Name": "49928ccb30e83351c4f84ae9f50d272f275d3d2baa50a419b03e523a3fbcc96c",
                "Source": "/var/lib/docker/volumes/49928ccb30e83351c4f84ae9f50d272f275d3d2baa50a419b03e523a3fbcc96c/_data",
                "Destination": "/usr/local/tomcat/webapps",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }
        ],
        "Config": {
            "Hostname": "1ea64d3c6cfa",
            "Domainname": "",
...

"Source": "/var/lib/docker/volumes/49928ccb30e83351c4f84ae9f50d272f275d3d2baa50a419b03e523a3fbcc96c/_data": 宿主机路径

"Destination": "/usr/local/tomcat/webapps": docker容器内路径

6.docker build命令

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[root@localhost docker]# docker build --help

Usage:  docker build [OPTIONS] PATH | URL | -

Build an image from a Dockerfile

Options:
      --build-arg list             Set build-time variables (default [])
      --cache-from stringSlice     Images to consider as cache sources
      --cgroup-parent string       Optional parent cgroup for the container
      --compress                   Compress the build context using gzip
      --cpu-period int             Limit the CPU CFS (Completely Fair Scheduler) period
      --cpu-quota int              Limit the CPU CFS (Completely Fair Scheduler) quota
  -c, --cpu-shares int             CPU shares (relative weight)
      --cpuset-cpus string         CPUs in which to allow execution (0-3, 0,1)
      --cpuset-mems string         MEMs in which to allow execution (0-3, 0,1)
      --disable-content-trust      Skip image verification (default true)
  -f, --file string                Name of the Dockerfile (Default is 'PATH/Dockerfile')
      --force-rm                   Always remove intermediate containers
      --help                       Print usage
      --isolation string           Container isolation technology
      --label list                 Set metadata for an image (default [])
  -m, --memory string              Memory limit
      --memory-swap string         Swap limit equal to memory plus swap: '-1' to enable unlimited swap
      --network string             Set the networking mode for the RUN instructions during build (default "default")
      --no-cache                   Do not use cache when building the image
      --pull                       Always attempt to pull a newer version of the image
  -q, --quiet                      Suppress the build output and print image ID on success
      --rm                         Remove intermediate containers after a successful build (default true)
      --security-opt stringSlice   Security options
      --shm-size string            Size of /dev/shm, default value is 64MB
  -t, --tag list                   Name and optionally a tag in the 'name:tag' format (default [])
      --ulimit ulimit              Ulimit options (default [])
  -v, --volume list                Set build-time bind mounts (default [])

4，数据卷容器

4.1，作用

数据卷容器: 实现容器之间的数据共享

不同的容器都指向宿主机中的同一个路径，删除其中的一个容器不影响指向的宿主机中的路径

4.2，实例

  1. 创建Dockerfile

使用Dockerfile构造镜像，生成一个自定义的centos

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# 基于centos构造一个镜像
FROM centos
# 加入容器卷
VOLUME ["/usr/local/mydata"]
CMD echo "finished successfully"
CMD /bin/bash
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[root@localhost docker]# docker build -t mycentos01:1.0 .

output:

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Sending build context to Docker daemon 2.048 kB
Step 1/4 : FROM centos
 ---> 0d120b6ccaa8
Step 2/4 : VOLUME /usr/local/mydata
 ---> Running in 415dbf119a9b
 ---> db4f8cdb476f
Removing intermediate container 415dbf119a9b
Step 3/4 : CMD echo "finished successfully"
 ---> Running in 79454fdd84c2
 ---> a3a51fa2bd36
Removing intermediate container 79454fdd84c2
Step 4/4 : CMD /bin/bash
 ---> Running in 43561372addb
 ---> 9aea850e12d7
Removing intermediate container 43561372addb
Successfully built 9aea850e12d7
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[root@localhost docker]# docker images
REPOSITORY              TAG                 IMAGE ID            CREATED             SIZE
mycentos01              1.0                 9aea850e12d7        5 seconds ago       215 MB
  1. 使用自己创建的镜像启动一个容器
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[root@localhost docker]# docker run -it --name=centos1 mycentos01:1.0 /bin/bash

[root@localhost docker]# docker run -it -d --name=centos3 --volumes-from centos2 mycentos01:1.0 /bin/bash

--volumes-from: 继承

使用自己创建的镜像启动第二个容器继承第一个

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[root@localhost docker]# docker run -it -d --name=centos2 --volumes-from centos1 mycentos01:1.0 /bin/bash

使用自己创建的镜像启动第三个容器继承第二个

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[root@localhost docker]# docker run -it -d --name=centos3 --volumes-from centos2 mycentos01:1.0 /bin/bash

output: 

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[root@localhost docker]# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED              STATUS              PORTS                    NAMES
00bc4c3a9b49        mycentos01:1.0      "/bin/bash"         4 seconds ago        Up 3 seconds                                 centos3
43dabcee22ec        mycentos01:1.0      "/bin/bash"         About a minute ago   Up About a minute                            centos2
4a0a0d288acf        mycentos01:1.0      "/bin/bash"         4 minutes ago        Up 4 minutes                                 centos1
  1. 测试方法

进入centos1，在mydata里面创建个centos1.txt

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[root@localhost docker]# docker exec -it centos1 /bin/bash
[root@4a0a0d288acf mydata]# touch centos1.txt
[root@4a0a0d288acf mydata]# echo "make file in centos1" > centos1.txt
[root@4a0a0d288acf mydata]# cat centos1.txt
make file in centos1

进入centos2，查看mydata里面也有centos1.txt，在centos2的mydata里面创建centos2.txt

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[root@localhost docker]# docker exec -it centos2 /bin/bash
[root@43dabcee22ec /]# cd /usr/local/mydata/
[root@43dabcee22ec mydata]# ls
centos1.txt
[root@43dabcee22ec mydata]# cat centos1.txt
make file in centos1
[root@43dabcee22ec mydata]# echo "make file in centos2" > centos2.txt
[root@43dabcee22ec mydata]# ls
centos1.txt  centos2.txt
[root@43dabcee22ec mydata]# cat centos2.txt
make file in centos2

进入centos3查看mydata里面的数据，可以找到centos1.txt和centos2.txt

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[root@localhost docker]# docker exec -it centos3 /bin/bash
[root@00bc4c3a9b49 /]# cd /usr/local/mydata/
[root@00bc4c3a9b49 mydata]# ls
centos1.txt  centos2.txt
[root@00bc4c3a9b49 mydata]# echo "make file in centos3" > centos3.txt
[root@00bc4c3a9b49 mydata]# ls
centos1.txt  centos2.txt  centos3.txt

在centos1里也可以找到centos2.txt和centos3.txt

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[root@localhost docker]# docker exec -it centos1 /bin/bash
[root@4a0a0d288acf /]# cd /usr/local/mydata/
[root@4a0a0d288acf mydata]# ls
centos1.txt  centos2.txt  centos3.txt

删除os1之后情况，centos2和centos3的mydata里面的数据不会发生变化，因为不同的容器都指向宿主机中的同一个路径，删除其中的一个容器不影响其他容器指向的宿主机中的路径

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[root@localhost docker]# docker rm -f centos1
centos1
[root@localhost docker]# docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS                    NAMES
00bc4c3a9b49        mycentos01:1.0      "/bin/bash"         15 minutes ago      Up 15 minutes                                centos3
43dabcee22ec        mycentos01:1.0      "/bin/bash"         16 minutes ago      Up 16 minutes                                centos2
[root@localhost docker]# docker exec -it centos2 /bin/bash
[root@43dabcee22ec /]# cd /usr/local/mydata/
[root@43dabcee22ec mydata]# ls
centos1.txt  centos2.txt  centos3.txt