docker之Dockerfile实践

陌路拾爱 發表於 2017-11-1 17:50:00

上一篇介绍了Dockerfile中使用的指令，现在开始进行指令实践
先查看下本地的镜像，选一个作为base image：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
在某一个目录下面创建一个专门存放此demo的目录，也就是Dockerfile所在的context：
<div class="cnblogs_code">
<pre># mkdir docker_demo
# cd docker_demo/
# touch Dockerfile
# pwd
/root/docker_demo
# ll
total 0
-rw-r--r--. 1 root root 0 Nov1 04:34 Dockerfile</pre>
</div>
接下来就开始编写Dockerfile文件了（注意Dockerfile的D需要大写）
这里以编译nginx提供web服务来构建新的镜像
1、下载nginx源码包到docker_demo这个目录下：
<div class="cnblogs_code">
<pre># ll
total 960
-rw-r--r--. 1 root root 0 Nov1 04:34 Dockerfile
-rw-r--r--. 1 root root 981687 Oct 17 09:20 nginx-1.12.2.tar.gz</pre>
</div>
2、以下是编写好的Dockerfile v1版：
<div class="cnblogs_code">
# 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
EXPOSE 80

</div>
3、查看docker_demo目录情况：
<div class="cnblogs_code">
<pre># ll
total 964
-rw-r--r--. 1 root root 1112 Nov1 04:58 Dockerfile
-rw-r--r--. 1 root root 981687 Oct 17 09:20 nginx-1.12.2.tar.gz</pre>
</div>
4、执行docker build进行构建：
<div class="cnblogs_code">
<pre>docker build -t centos_nginx:v1 .</pre>
</div>
后面的.代表的是相对路径的当前目录，如果需要全路径则为/root/docker_demo（就是找到Dockerfile文件）
构建成功后，查看新构建的镜像：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
5、然后使用构建的镜像启动一个container并开启nginx服务：
<div class="cnblogs_code">
<pre># docker run -d centos_nginx:v1 /usr/local/nginx/sbin/nginx -g "daemon off;"
ea5af922378356a5ebff60992f000b186b09d1e8d6a4915b0b8ccf997ca12404</pre>
</div>
然后查看启动的container是否在运行：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
虽然nginx服务开启了，但是port并没有进行映射到本机host，所以这个container并不能进行访问，重新启动一个进行了映射端口的容器
<div class="cnblogs_code">
<pre># docker run -d -p80:80 centos_nginx:v1 /usr/local/nginx/sbin/nginx -g "daemon off;"
e4b6e4846dedc6f130e028701c84828a635f3b367c0d500ebd947de16b1be0b2</pre>
</div>
再次查看端口映射信息：
<div class="cnblogs_code">
<pre># docker port e4b6e4846ded
80/tcp -> 0.0.0.0:80</pre>
</div>
于是进行访问：
<img src="https://images2017.cnblogs.com/blog/1168897/201711/1168897-20171101214944701-2097058657.png" alt="">
于是基于Dockerfile的一个简单实例构建完成，现在基于这个Dockerfile文件依次添加其他的指令进行构建
添加ENV环境变量指令：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
然后进行构建：
<div class="cnblogs_code">
<pre># docker build -t centos_nginx:v2 .
Sending build context to Docker daemon985.6kB
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:$PATH
---> Running in 07ba2f7129bc
---> 9588fa1058aa
Removing intermediate container 07ba2f7129bc
Step 10/10 : EXPOSE 80
---> Running in 473cd847154a
---> 2031faf8894a
Removing intermediate container 473cd847154a
Successfully built 2031faf8894a
Successfully tagged centos_nginx:v2</pre>
</div>
由于在构建的过程中docker会采用缓存的机制，上面的构建过程中包含很多using cache，所以这次构建非常快，如果需要重新构建，不想使用cache需要添加--no-cache
--no-cache                   Do not use cache when building the image
查看v2版本的镜像：
<div class="cnblogs_code">
<pre># docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos_nginx v2 2031faf8894a 2 minutes ago 464MB</pre>
</div>
使用v2版本的镜像启动一个container：
<div class="cnblogs_code">
<pre># docker run -d -p81:80 centos_nginx:v2 nginx -g "daemon off;"
da48b465b1b1a14824497d724eee52b8408270b3b5223c5dd7094b7c0cef211d</pre>
</div>
查看container运行状态：
<div class="cnblogs_code">
<pre># docker ps -l
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
da48b465b1b1 centos_nginx:v2 "nginx -g 'daemon ..." 23 seconds ago Up 22 seconds 0.0.0.0:81->80/tcp determined_neumann</pre>
</div>
进行访问：
<img src="https://images2017.cnblogs.com/blog/1168897/201711/1168897-20171101215815091-474688798.png" alt="">
上述启动容器的过程中使用的命令docker run -d -p81:80 centos_nginx:v2 nginx -g "daemon off;"为什么这里使用的nginx而不是
/usr/local/nginx/sbin/nginx，因为在Dockerfile文化中执行了PATH=/usr/local/nginx/sbin:$PATH，添加到了环境变量
 
添加指令CMD：
<div class="cnblogs_code">
<pre># 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;"'</pre>
</div>
然后进行构建：
<div class="cnblogs_code">
<pre># docker build -t centos_nginx:v3 .</pre>
</div>
查看v3版本的镜像：
<div class="cnblogs_code">
<pre># docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos_nginx v3 0e49a2c0562f 11 seconds ago 464MB</pre>
</div>
然后基于v3版本的镜像启动一个container：
<div class="cnblogs_code">
<pre># docker run -d -p82:80 centos_nginx:v3
d988c04d04f49b909f28e7b664be3959a0d51b951f1c1b04fcf5c716552b7c41</pre>
</div>
查看启动的容器状态：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
最后进行访问：
<img src="https://images2017.cnblogs.com/blog/1168897/201711/1168897-20171101220437310-328967201.png" alt="">
新增加的CMD /bin/sh -c 'nginx -g "daemon off;"'表示
当启动一个container时默认运行的命令，如果在启动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：
<div class="cnblogs_code">
<pre># 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;"]</pre>
</div>
当ENTRYPOINT和CMD连用时，CMD的命令是ENTRYPOINT命令的参数，两者连用相当于nginx -g "daemon off;"
而当一起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，如果都是sh模式可以试一下）
开始进行构建v4版本：
<div class="cnblogs_code">
<pre># docker build -t centos_nginx:v4 .</pre>
</div>
查看新建的镜像：
<div class="cnblogs_code">
<pre># docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos_nginx v4 6c5128aaff05 4 minutes ago 464MB</pre>
</div>
为v4版本的镜像启动一个container：
<div class="cnblogs_code">
<pre># docker run -d -p83:80 centos_nginx:v4
6933c78255f3cebe44d4d5d080caf8a2fde45ded2f9b333ec01cdfe98cd5f417</pre>
</div>
然后查看容器状态：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
最后进行访问：
<img src="https://images2017.cnblogs.com/blog/1168897/201711/1168897-20171101222146232-1534714177.png" alt="">
这里增加一个案例，如果Dockerfile修改成下面：
<div class="cnblogs_code">
<pre># 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;"]</pre>
</div>
CMD的命令修改为了后台，我们知道如果容器内的进程在后台运行那么容器将不会运行，现在以此构建v5版本镜像：
<div class="cnblogs_code">
<pre># docker build -t centos_nginx:v5 .</pre>
</div>
查看v5版本的新镜像：
<div class="cnblogs_code">
<pre># docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos_nginx v5 5c1131306686 29 seconds ago 464MB</pre>
</div>
现在利用v5版本镜像启动一个container，但是在启动的时候添加后面的command：
<div class="cnblogs_code">
<pre># docker run -d -p85:80 centos_nginx:v5 -g "daemon off;"
5e11edbbd2a0e184f1766c435c0d9b01ef5d74b57e2e2c3a1efed0cf2a2e037b</pre>
</div>
可以看见在后面新增了-g "daemon off;"，前面说过如果增加了命令那么Dockerfile中的CMD中的命令将不会生效
查看容器运行状态：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
可以看见容器的运行丝毫没有问题，于是nginx的服务依然还是在前台运行，没有被CMD影响，而新增加的command（-g "daemon off;"）
将作为ENTRYPOINT的新的参数以此为准，于是进行访问端口85
<img src="https://images2017.cnblogs.com/blog/1168897/201711/1168897-20171101222929201-743437922.png" alt="">
 添加VOLUME指令：
<div class="cnblogs_code">
<pre># 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"]</pre>
</div>
开始进行构建：
<div class="cnblogs_code">
<pre># docker build -t centos_nginx:v6 .</pre>
</div>
查看v6版本的镜像：
<div class="cnblogs_code">
<pre># docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
centos_nginx v6 959fdf4d4288 35 seconds ago 464MB</pre>
</div>
利用该镜像启动一个container：
<div class="cnblogs_code">
<pre># docker run -d -p 86:80 --name=nginx6 centos_nginx:v6 -g "daemon off;"
6c15a9e93fb1421bdb7eddaabe439996e97415e85a003f80c1d8b4b2c5ee3ffa</pre>
</div>
查看启动的容器状态：
<div class="cnblogs_code">
<pre># 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</pre>
</div>
利用docker exec进入到container中，查看是否存在卷/data：
<div class="cnblogs_code">
<pre># 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 Nov2 01:42 data</pre>
</div>
这个/data挂载的目录对应本机host的这个目录：
<div class="cnblogs_code">
<pre># pwd
/var/lib/docker/volumes/3490a9b7f9773b020343e82c1c4236d976b69eb6a80121eb80612d8c39e02820/_data</pre>
</div>
现在在本机host上的这个目录创建一个文件：
<div class="cnblogs_code">
<pre># touch wadeson.sh
# ll
total 0
-rw-r--r--. 1 root root 0 Nov1 21:45 wadeson.sh</pre>
</div>
然后切换到container中查看是否存在这个文件：
<div class="cnblogs_code">
<pre># ll /data/
total 0
-rw-r--r--. 1 root root 0 Nov2 01:45 wadeson.sh</pre>
</div>
 
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
<div class="cnblogs_code">
<pre># 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"]</pre>
</div>
使用上面Dockerfile构建镜像版本v7：
<div class="cnblogs_code">
<pre># docker run -d -p 87:80 --name=nginx7 centos_nginx:v7 -g "daemon off;"
48f1fe5c71aefc0f9513e8085af8f5b7cdf14fa986fb3b11f2050f18ceefd26e</pre>
</div>
现在进入到容器内查看是否存在/data：
<div class="cnblogs_code">
<pre># docker exec -it nginx7 /bin/bash
# ll /data
ls: cannot access /data: No such file or directory</pre>
</div>
现在修改上面Dockerfile的FROM基于的base image：
<div class="cnblogs_code">
# cat Dockerfile # base image FROM centos_nginx:v7
# MAINTAINER MAINTAINER json_hc@163.com
</div>
利用此Dockerfile构建镜像v8：
<div class="cnblogs_code">
<pre># docker build -t centos_nginx:v8 .
Sending build context to Docker daemon986.6kB
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</pre>
</div>
可以看见卷/data已经执行了操作，现在启动一个container：
<div class="cnblogs_code">
<pre># docker run -d -p 88:80 --name=nginx8 centos_nginx:v8 -g "daemon off;"
6c2a847c5f6b59b02f91afecadbfc15c88d1217a477c0421a424bce6e5eb317a</pre>
</div>
查看容器状态，并进入到容器验证/data目录：
<div class="cnblogs_code">
<pre># 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
# docker exec -it nginx8 /bin/bash
# ll /data/
total 0</pre>
</div>
由此可见镜像v8包含了v7 的所有内容，并且增加了ONBUILD的内容 
来源：https://www.cnblogs.com/jsonhc/p/7767669.html

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docker之Dockerfile实践