docker之Dockerfile实践

时间 2019-11-21

原文原文链接

上一篇介绍了Dockerfile中使用的指令，如今开始进行指令实践nginx

先查看下本地的镜像，选一个做为base image：c++

[root@docker ~]# docker images
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
wadeson/centos_nginx   v1                  210a202d37b8        2 hours ago         464MB
nginx                  latest              c59f17fe53b0        4 days ago          108MB
ubuntu                 latest              747cb2d60bbe        3 weeks ago         122MB
centos                 latest              196e0ce0c9fb        6 weeks ago         197MB

在某一个目录下面建立一个专门存放此demo的目录，也就是Dockerfile所在的context：web

[root@docker ~]# mkdir docker_demo
[root@docker ~]# cd docker_demo/
[root@docker docker_demo]# touch Dockerfile
[root@docker docker_demo]# pwd
/root/docker_demo
[root@docker docker_demo]# ll
total 0
-rw-r--r--. 1 root root 0 Nov  1 04:34 Dockerfile

接下来就开始编写Dockerfile文件了（注意Dockerfile的D须要大写）docker

这里以编译nginx提供web服务来构建新的镜像json

一、下载nginx源码包到docker_demo这个目录下：ubuntu

[root@docker docker_demo]# ll
total 960
-rw-r--r--. 1 root root      0 Nov  1 04:34 Dockerfile
-rw-r--r--. 1 root root 981687 Oct 17 09:20 nginx-1.12.2.tar.gz

二、如下是编写好的Dockerfile v1版：centos

[root@docker docker_demo]# cat Dockerfile
# base image
FROM centos缓存

# MAINTAINER
MAINTAINER json_hc@163.combash

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/srcdom

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio --with-http_ssl_module --with-http_realip_module --with-http_addition_module --with-http_xslt_module --with-http_image_filter_module --with-http_geoip_module --with-http_sub_module --with-http_dav_module --with-http_flv_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_auth_request_module --with-http_random_index_module --with-http_secure_link_module --with-http_degradation_module --with-http_stub_status_module && make && make install

EXPOSE 80

三、查看docker_demo目录状况：

[root@docker docker_demo]# ll
total 964
-rw-r--r--. 1 root root   1112 Nov  1 04:58 Dockerfile
-rw-r--r--. 1 root root 981687 Oct 17 09:20 nginx-1.12.2.tar.gz

四、执行docker build进行构建：

docker build -t centos_nginx:v1 .

后面的.表明的是相对路径的当前目录，若是须要全路径则为/root/docker_demo（就是找到Dockerfile文件）

构建成功后，查看新构建的镜像：

[root@docker docker_demo]# docker images         
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
centos_nginx           v1                  78d18f16e757        4 hours ago         464MB
wadeson/centos_nginx   v1                  210a202d37b8        7 hours ago         464MB
nginx                  latest              c59f17fe53b0        4 days ago          108MB
ubuntu                 latest              747cb2d60bbe        3 weeks ago         122MB
centos                 latest              196e0ce0c9fb        6 weeks ago         197MB

五、而后使用构建的镜像启动一个container并开启nginx服务：

[root@docker docker_demo]# docker run -d centos_nginx:v1 /usr/local/nginx/sbin/nginx -g "daemon off;"
ea5af922378356a5ebff60992f000b186b09d1e8d6a4915b0b8ccf997ca12404

而后查看启动的container是否在运行：

[root@docker docker_demo]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
ea5af9223783        centos_nginx:v1     "/usr/local/nginx/..."   7 seconds ago       Up 6 seconds        80/tcp              flamboyant_carson

虽然nginx服务开启了，可是port并无进行映射到本机host，因此这个container并不能进行访问，从新启动一个进行了映射端口的容器

[root@docker docker_demo]# docker run -d -p80:80 centos_nginx:v1 /usr/local/nginx/sbin/nginx -g "daemon off;"
e4b6e4846dedc6f130e028701c84828a635f3b367c0d500ebd947de16b1be0b2

再次查看端口映射信息：

[root@docker docker_demo]# docker port e4b6e4846ded
80/tcp -> 0.0.0.0:80

因而进行访问：

因而基于Dockerfile的一个简单实例构建完成，如今基于这个Dockerfile文件依次添加其余的指令进行构建

添加ENV环境变量指令：

[root@docker docker_demo]# cat Dockerfile 
# base image
FROM centos

# MAINTAINER
MAINTAINER json_hc@163.com

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/src

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel 
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install

ENV PATH /usr/local/nginx/sbin:$PATH

EXPOSE 80

而后进行构建：

[root@docker docker_demo]# docker build -t centos_nginx:v2 .
Sending build context to Docker daemon  985.6kB
Step 1/10 : FROM centos
 ---> 196e0ce0c9fb
Step 2/10 : MAINTAINER json_hc@163.com
 ---> Using cache
 ---> cde1d7830106
Step 3/10 : ADD nginx-1.12.2.tar.gz /usr/local/src
 ---> Using cache
 ---> 1e4d16340af0
Step 4/10 : RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel
 ---> Using cache
 ---> 405835ad9b0b
Step 5/10 : RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
 ---> Using cache
 ---> 4002738cf7a6
Step 6/10 : RUN useradd -M -s /sbin/nologin nginx
 ---> Using cache
 ---> 02961c5c564d
Step 7/10 : WORKDIR /usr/local/src/nginx-1.12.2
 ---> Using cache
 ---> f1da71a93c5e
Step 8/10 : RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install
 ---> Using cache
 ---> cd2ad4c45004
Step 9/10 : ENV PATH /usr/local/nginx/sbin:$PATH
 ---> Running in 07ba2f7129bc
 ---> 9588fa1058aa
Removing intermediate container 07ba2f7129bc
Step 10/10 : EXPOSE 80
 ---> Running in 473cd847154a
 ---> 2031faf8894a
Removing intermediate container 473cd847154a
Successfully built 2031faf8894a
Successfully tagged centos_nginx:v2

因为在构建的过程当中docker会采用缓存的机制，上面的构建过程当中包含不少using cache，因此此次构建很是快，若是须要从新构建，不想使用cache须要添加--no-cache

--no-cache Do not use cache when building the image

查看v2版本的镜像：

[root@docker docker_demo]# docker images
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
centos_nginx           v2                  2031faf8894a        2 minutes ago       464MB

使用v2版本的镜像启动一个container：

[root@docker docker_demo]# docker run -d -p81:80 centos_nginx:v2 nginx -g "daemon off;"
da48b465b1b1a14824497d724eee52b8408270b3b5223c5dd7094b7c0cef211d

查看container运行状态：

[root@docker docker_demo]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
da48b465b1b1        centos_nginx:v2     "nginx -g 'daemon ..."   23 seconds ago      Up 22 seconds       0.0.0.0:81->80/tcp   determined_neumann

进行访问：

上述启动容器的过程当中使用的命令docker run -d -p81:80 centos_nginx:v2 nginx -g "daemon off;"为何这里使用的nginx而不是

/usr/local/nginx/sbin/nginx，由于在Dockerfile文化中执行了PATH=/usr/local/nginx/sbin:$PATH，添加到了环境变量

添加指令CMD：

[root@docker docker_demo]# cat Dockerfile 
# base image
FROM centos

# MAINTAINER
MAINTAINER json_hc@163.com

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/src

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel 
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install

ENV PATH /usr/local/nginx/sbin:$PATH

EXPOSE 80

CMD /bin/sh -c 'nginx -g "daemon off;"'

而后进行构建：

[root@docker docker_demo]# docker build -t centos_nginx:v3 .

查看v3版本的镜像：

[root@docker docker_demo]# docker images
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
centos_nginx           v3                  0e49a2c0562f        11 seconds ago      464MB

而后基于v3版本的镜像启动一个container：

[root@docker docker_demo]# docker run -d -p82:80 centos_nginx:v3 
d988c04d04f49b909f28e7b664be3959a0d51b951f1c1b04fcf5c716552b7c41

查看启动的容器状态：

[root@docker docker_demo]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
d988c04d04f4        centos_nginx:v3     "/bin/sh -c '/bin/..."   6 seconds ago       Up 5 seconds        0.0.0.0:82->80/tcp   optimistic_saha

最后进行访问：

新增长的CMD /bin/sh -c 'nginx -g "daemon off;"'表示

当启动一个container时默认运行的命令，若是在启动container时赋予了command的化，那么

定义的CMD中的命令将不会被执行，而会去执行command的命令

添加entrypoint指令：

[root@docker docker_demo]# cat Dockerfile 
# base image
FROM centos

# MAINTAINER
MAINTAINER json_hc@163.com

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/src

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel 
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install

ENV PATH /usr/local/nginx/sbin:$PATH

EXPOSE 80

ENTRYPOINT ["nginx"]

CMD ["-g","daemon off;"]

当ENTRYPOINT和CMD连用时，CMD的命令是ENTRYPOINT命令的参数，二者连用至关于nginx -g "daemon off;"

而当一块儿连用的时候命令格式最好一致（这里选择的都是json格式的是成功的，若是都是sh模式能够试一下）

开始进行构建v4版本：

[root@docker docker_demo]# docker build -t centos_nginx:v4 .

查看新建的镜像：

[root@docker docker_demo]# docker images
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
centos_nginx           v4                  6c5128aaff05        4 minutes ago       464MB

为v4版本的镜像启动一个container：

[root@docker docker_demo]# docker run -d -p83:80 centos_nginx:v4 
6933c78255f3cebe44d4d5d080caf8a2fde45ded2f9b333ec01cdfe98cd5f417

而后查看容器状态：

[root@docker docker_demo]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
6933c78255f3        centos_nginx:v4     "nginx -g 'daemon ..."   6 seconds ago       Up 5 seconds        0.0.0.0:83->80/tcp   zealous_euclid

最后进行访问：

这里增长一个案例，若是Dockerfile修改为下面：

[root@docker docker_demo]# cat Dockerfile 
# base image
FROM centos

# MAINTAINER
MAINTAINER json_hc@163.com

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/src

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel 
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install

ENV PATH /usr/local/nginx/sbin:$PATH

EXPOSE 80

ENTRYPOINT ["nginx"]

CMD ["-g","daemon on;"]

CMD的命令修改成了后台，咱们知道若是容器内的进程在后台运行那么容器将不会运行，如今以此构建v5版本镜像：

[root@docker docker_demo]# docker build -t centos_nginx:v5 .

查看v5版本的新镜像：

[root@docker docker_demo]# docker images
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
centos_nginx           v5                  5c1131306686        29 seconds ago      464MB

如今利用v5版本镜像启动一个container，可是在启动的时候添加后面的command：

[root@docker docker_demo]# docker run -d -p85:80 centos_nginx:v5 -g "daemon off;"
5e11edbbd2a0e184f1766c435c0d9b01ef5d74b57e2e2c3a1efed0cf2a2e037b

能够看见在后面新增了-g "daemon off;"，前面说过若是增长了命令那么Dockerfile中的CMD中的命令将不会生效

查看容器运行状态：

[root@docker docker_demo]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
5e11edbbd2a0        centos_nginx:v5     "nginx -g 'daemon ..."   3 seconds ago       Up 3 seconds        0.0.0.0:85->80/tcp   nifty_bartik

能够看见容器的运行丝毫没有问题，因而nginx的服务依然仍是在前台运行，没有被CMD影响，而新增长的command（-g "daemon off;"）

将做为ENTRYPOINT的新的参数以此为准，因而进行访问端口85

添加VOLUME指令：

[root@docker docker_demo]# cat Dockerfile 
# base image
FROM centos

# MAINTAINER
MAINTAINER json_hc@163.com

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/src

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel 
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# mount a dir to container
VOLUME ["/data"]

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install

# setup PATH
ENV PATH /usr/local/nginx/sbin:$PATH

# EXPOSE
EXPOSE 80

# the command of entrypoint
ENTRYPOINT ["nginx"]

CMD ["-g"]

开始进行构建：

[root@docker docker_demo]# docker build -t centos_nginx:v6 .

查看v6版本的镜像：

[root@docker ~]# docker images
REPOSITORY             TAG                 IMAGE ID            CREATED             SIZE
centos_nginx           v6                  959fdf4d4288        35 seconds ago      464MB

利用该镜像启动一个container：

[root@docker ~]# docker run -d -p 86:80 --name=nginx6 centos_nginx:v6 -g "daemon off;"
6c15a9e93fb1421bdb7eddaabe439996e97415e85a003f80c1d8b4b2c5ee3ffa

查看启动的容器状态：

[root@docker ~]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
6c15a9e93fb1        centos_nginx:v6     "nginx -g 'daemon ..."   4 seconds ago       Up 4 seconds        0.0.0.0:86->80/tcp   nginx6

利用docker exec进入到container中，查看是否存在卷/data：

[root@6c15a9e93fb1 /]# ll
total 16
-rw-r--r--.   8 root root 15836 Sep 11 15:53 anaconda-post.log
lrwxrwxrwx.   1 root root     7 Sep 11 15:51 bin -> usr/bin
drwxr-xr-x.   2 root root     6 Nov  2 01:42 data

这个/data挂载的目录对应本机host的这个目录：

[root@docker _data]# pwd
/var/lib/docker/volumes/3490a9b7f9773b020343e82c1c4236d976b69eb6a80121eb80612d8c39e02820/_data

如今在本机host上的这个目录建立一个文件：

[root@docker _data]# touch wadeson.sh
[root@docker _data]# ll
total 0
-rw-r--r--. 1 root root 0 Nov  1 21:45 wadeson.sh

而后切换到container中查看是否存在这个文件：

[root@6c15a9e93fb1 /]# ll /data/
total 0
-rw-r--r--. 1 root root 0 Nov  2 01:45 wadeson.sh

添加ONBUILD指令：

　　Dockerfile1中base image为A镜像，并在Dockerfile1中定义ONBUILD指令，构建成新镜像B镜像

　　Dockerfile2中base image为B镜像，构建成新镜像C

　　当使用镜像B启动的container1不会执行OBNUILD中定义的内容，而使用C镜像启动的container2则会执行ONBUILD定义的内容

[root@docker docker_demo]# cat Dockerfile 
# base image
FROM centos

# MAINTAINER
MAINTAINER json_hc@163.com

# put nginx-1.12.2.tar.gz into /usr/local/src and unpack nginx
ADD nginx-1.12.2.tar.gz /usr/local/src

# running required command
RUN yum install -y gcc gcc-c++ glibc make autoconf openssl openssl-devel 
RUN yum install -y libxslt-devel -y gd gd-devel GeoIP GeoIP-devel pcre pcre-devel
RUN useradd -M -s /sbin/nologin nginx

# mount a dir to container
ONBUILD VOLUME ["/data"]

# change dir to /usr/local/src/nginx-1.12.2
WORKDIR /usr/local/src/nginx-1.12.2

# execute command to compile nginx
RUN ./configure --user=nginx --group=nginx --prefix=/usr/local/nginx --with-file-aio  --with-http_ssl_module  --with-http_realip_module    --with-http_addition_module    --with-http_xslt_module   --with-http_image_filter_module    --with-http_geoip_module  --with-http_sub_module  --with-http_dav_module --with-http_flv_module    --with-http_mp4_module --with-http_gunzip_module  --with-http_gzip_static_module  --with-http_auth_request_module  --with-http_random_index_module   --with-http_secure_link_module   --with-http_degradation_module   --with-http_stub_status_module && make && make install

# setup PATH
ENV PATH /usr/local/nginx/sbin:$PATH

# EXPOSE
EXPOSE 80

# the command of entrypoint
ENTRYPOINT ["nginx"]

CMD ["-g"]

使用上面Dockerfile构建镜像版本v7：

[root@docker docker_demo]# docker run -d -p 87:80 --name=nginx7 centos_nginx:v7 -g "daemon off;"   
48f1fe5c71aefc0f9513e8085af8f5b7cdf14fa986fb3b11f2050f18ceefd26e

如今进入到容器内查看是否存在/data：

[root@docker ~]# docker exec -it nginx7 /bin/bash
[root@48f1fe5c71ae nginx-1.12.2]# ll /data
ls: cannot access /data: No such file or directory

如今修改上面Dockerfile的FROM基于的base image：

[root@docker docker_demo]# cat Dockerfile
# base image
FROM centos_nginx:v7

# MAINTAINER
MAINTAINER json_hc@163.com

利用此Dockerfile构建镜像v8：

[root@docker docker_demo]# docker build -t centos_nginx:v8 .
Sending build context to Docker daemon  986.6kB
Step 1/2 : FROM centos_nginx:v7
# Executing 1 build trigger...
Step 1/1 : VOLUME /data
 ---> Running in a6187867513d
 ---> 5ac07930be4c
Removing intermediate container a6187867513d
Step 2/2 : MAINTAINER json_hc@163.com
 ---> Running in e02dbf8219cf
 ---> 6f792dc07c35
Removing intermediate container e02dbf8219cf
Successfully built 6f792dc07c35
Successfully tagged centos_nginx:v8

能够看见卷/data已经执行了操做，如今启动一个container：

[root@docker docker_demo]# docker run -d -p 88:80 --name=nginx8 centos_nginx:v8 -g "daemon off;"   
6c2a847c5f6b59b02f91afecadbfc15c88d1217a477c0421a424bce6e5eb317a

查看容器状态，并进入到容器验证/data目录：

[root@docker docker_demo]# docker ps -l
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                NAMES
6c2a847c5f6b        centos_nginx:v8     "nginx -g 'daemon ..."   37 seconds ago      Up 37 seconds       0.0.0.0:88->80/tcp   nginx8
[root@docker docker_demo]# docker exec -it nginx8 /bin/bash
[root@6c2a847c5f6b nginx-1.12.2]# ll /data/
total 0

因而可知镜像v8包含了v7 的全部内容，而且增长了ONBUILD的内容