Dockerfile构建镜像

一、Dockerfile的条条框框

1、什么是Dockerfile？

Dockerfile是一种被Docker程序解释的脚本。Dockerfile由一条一条的指令组成，并且有自己的书写格式和支持的命令。当我们需要指定自己额外的需求时，只需在Dockerfile上添加或修改指令，然后通过docker build生成我们自定义的镜像（image）。

2、Dockerfile的注意事项

• Dockerfile的指令是忽略大小写的，建议使用大写
• 每一行只支持一条指令
• 每条指令可以携带多个参数
• 支持以#开头的注释

3、Dockerfile指令（instruction）

构建指令：用于构建image。其指定的操作不会在运行image的容器上执行（FROM、MAINTAINER、RUN、ENV、ADD、COPY）

设置指令：用于设置image的属性。其指定的操作将在运行image的容器中执行（CMD、ENTRYPOINT、USER 、EXPOSE、VOLUME、WORKDIR、ONBUILD）

4、Dockerfile的基本结构

基础镜像信息、维护者信息、镜像操作指令、容器启动时执行指令

二、Dockerfile指令（instruction）实操

1、FROM（指定基础image，必须为第一个命令）

格式：

FROM <image>
FROM <image>:
/<image>/<image>

例：

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
[root@localhost docker]# docker build -t my_test . #注意有个“.”
Sending build context to Docker daemon 2.048kB
Step 1/1 : FROM centos:latest
 ---> 9f38484d220f
Successfully built 9f38484d220f
Successfully tagged my_test:latest

2、MAINTAINER（维护者，用来指定创建者信息）

格式：

MAINTAINER <name>
/<name>

例：（通过inspect验证）

[root@localhost docker]# vim Dockerfile

#FROM centos

FROM centos:latest

MAINTAINER Xuyun Liu <[email protected]>

[root@localhost docker]# docker build -t my_test .

Sending build context to Docker daemon 2.048kB

Step 1/2 : FROM centos:latest

---> 9f38484d220f

Step 2/2 : MAINTAINER Xuyun Liu <[email protected]>

---> Using cache

---> be97dff9636f

Successfully built be97dff9636f

Successfully tagged my_test:latest

[root@localhost docker]# docker inspect -f {{.Author}} my_test

Xuyun Liu <[email protected]>

3、RUN（安装软件用）

格式：

RUN command param1 param2 #使用shell终端运行命令（/bin/sh、/bin/bash等）
RUN ['executable(可执行的))','param1（参数）','param2'...] #不通过shell执行，而是通过内建命令exec去执行

例：

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
MAINTAINER Xuyun Liu <[email protected]>
RUN touch /home/a.txt
RUN ["touch","/home/b.txt"] #这里双引号和单引号也是有讲究的，单引号会报错
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/4 : FROM centos:latest
 ---> 9f38484d220f
Step 2/4 : MAINTAINER Xuyun Liu <[email protected]>
 ---> Using cache
 ---> be97dff9636f
Step 3/4 : RUN touch /home/a.txt 

 ---> Using cache
 ---> 5af84bebdda1
Step 4/4 : RUN ["touch","/home/b.txt"]
 ---> Running in 541b7c7da76a
Removing intermediate container 541b7c7da76a
 ---> 6e19811bbf18
Successfully built 6e19811bbf18
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test ls /home
a.txt b.txt

4、CMD（设置container启动时执行的操作）

格式：

CMD command param1 param2
CMD ["executable","param1","param2"...]
CMD ["param1","param2"...] #当CMD和ENTRYPOINT配合使用时的写法

例1：CMD指令会被docker run提供的参数覆盖

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
CMD ls /dev
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/3 : FROM centos:latest
 ---> 9f38484d220f
Step 2/3 : RUN touch /home/a.txt
 ---> Running in 384f2554526a
Removing intermediate container 384f2554526a
 ---> cfb30d89ad46
Step 3/3 : CMD ls /dev
 ---> Running in b568167236d3
Removing intermediate container b568167236d3
 ---> 1e1971815006
Successfully built 1e1971815006
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test
console fd mqueue ptmx random stderr stdout urandom
core full null pts shm stdin tty zero 

[root@localhost docker]# docker run -it my_test ls /home
a.txt

例2：当一个Dockfile文件中有两个或多个CMD指令时，只执行最后一条CMD指令

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
CMD ls /dev
CMD ["ls","/usr","/usr/local"]
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/4 : FROM centos:latest
 ---> 9f38484d220f
Step 2/4 : RUN touch /home/a.txt
 ---> Using cache
 ---> cfb30d89ad46
Step 3/4 : CMD ls /dev
 ---> Using cache
 ---> 1e1971815006
Step 4/4 : CMD ["ls","/usr","/usr/local"]
 ---> Running in ccfabb87efc5
^[[ARemoving intermediate container ccfabb87efc5
 ---> e439603840ef
Successfully built e439603840ef
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test
/usr:
bin etc games include lib lib64 libexec local sbin share src tmp
/usr/local:
bin etc games include lib lib64 libexec sbin share src

5、ENTRYPOINT（设置container启动时执行的操作）

格式：

ENTRYPOINT command param1 param2
ENTRYPOINT ["executable","param1","param2"]

例1：ENTRYPOINT指令不会被docker run提供的参数覆盖

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
ENTRYPOINT ls /root /sys
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/3 : FROM centos:latest
 ---> 9f38484d220f
Step 2/3 : RUN touch /home/a.txt
 ---> Using cache
 ---> cfb30d89ad46
Step 3/3 : ENTRYPOINT ls /root /sys
 ---> Running in 67be0ac881cb
Removing intermediate container 67be0ac881cb
 ---> e51f45c181ac
Successfully built e51f45c181ac
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test
/root:
anaconda-ks.cfg
/sys:
block class devices fs kernel power
bus dev firmware hypervisor module
[root@localhost docker]# docker run -it my_test ls /home
/root:
anaconda-ks.cfg
/sys:
block class devices fs kernel power
bus dev firmware hypervisor module

例2：当一个Dockerfile文件中有两个或多个ENTRYPOINT指令时，只执行最后一条ENTRYPOINT指令

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
ENTRYPOINT ls /root /sys 

ENTRYPOINT ["ls","/home"]
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/4 : FROM centos:latest
 ---> 9f38484d220f
Step 2/4 : RUN touch /home/a.txt
 ---> Using cache
 ---> cfb30d89ad46
Step 3/4 : ENTRYPOINT ls /root /sys
 ---> Using cache
 ---> e51f45c181ac
Step 4/4 : ENTRYPOINT ["ls","/home"]
 ---> Running in 95c2491f9b3b
Removing intermediate container 95c2491f9b3b
 ---> 6196eaff66d3
Successfully built 6196eaff66d3
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test
a.txt

例3：当一个Dockerfile文件中既有CMD指令又有ENTRYPOINT指令时，CMD指令将被作为ENTRYPOINT指令的参数

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
#ENTRYPOINT ls /root /sys
CMD ["-l"]
ENTRYPOINT ["ls","/home"]
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/4 : FROM centos:latest
 ---> 9f38484d220f
Step 2/4 : RUN touch /home/a.txt
 ---> Using cache
 ---> cfb30d89ad46
Step 3/4 : CMD ["-l"]
 ---> Using cache
 ---> 4c5cf79c279d
Step 4/4 : ENTRYPOINT ["ls","/home"]
 ---> Using cache
 ---> 14d643d73d81
Successfully built 14d643d73d81 

Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test
total 0
-rw-r--r-- 1 root root 0 Aug 29 17:09 a.txt

6、USER（设置container的用户，默认是root用户，这个root不是那个root）

格式：

USER username/uid

例：

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
#RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
#ENTRYPOINT ls /root /sys
#CMD ["-l"]
#ENTRYPOINT ["ls","/home"]
RUN useradd admin #需要先创建一个用户，不然会提示用户不存在
USER admin
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/3 : FROM centos:latest
 ---> 9f38484d220f
Step 2/3 : RUN useradd admin
 ---> Running in a4847a39ab06
Removing intermediate container a4847a39ab06
 ---> 3759bdc0589c
Step 3/3 : USER admin
 ---> Running in 80e367ffe699
Removing intermediate container 80e367ffe699
 ---> c95196915358
Successfully built c95196915358
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test /bin/bash
[admin@f0f565e8da5a /]$ 

7、EXPOSE（暴露，指定容器需要映射到宿主机的端口）

格式：

EXPOSE port1 [port2 ...]

例：

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
#RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
#ENTRYPOINT ls /root /sys
#CMD ["-l"]
#ENTRYPOINT ["ls","/home"]
#RUN useradd admin
#USER admin
EXPOSE 80
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/2 : FROM centos:latest
 ---> 9f38484d220f
Step 2/2 : EXPOSE 80
 ---> Running in 75dda1ff5393
Removing intermediate container 75dda1ff5393
 ---> f6759e9df32d
Successfully built f6759e9df32d
Successfully tagged my_test:latest
[root@localhost docker]# docker run -dit -p 80 my_test /bin/bash #随机映射
5b790387fd758115204ce0a1f7ed1daa17a983108004948cb26b81f8fa8dc1f6 #随机映射（大P）
[root@localhost docker]# docker run -dit -P my_test /bin/bash #映射到宿主机的80
7207f9ae8a2c2932df727854cecb6b16d6b09ffecd1411bf42d03ffb1c271803
[root@localhost docker]# docker run -dit -p 80:80 my_test /bin/bash
83c40826648c13d23c706db3474d1eb541261638e5c1415abaebfb7a37d758ca
[root@localhost docker]# docker ps 
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
83c40826648c my_test "/bin/bash" About a minute ago Up About a minute 0.0.0.0:80->80/tcp silly_snyder
7207f9ae8a2c my_test "/bin/bash" 2 minutes ago Up 2 minutes 0.0.0.0:32769->80/tcp youthful_kirch
5b790387fd75 my_test "/bin/bash" 2 minutes ago Up 2 minutes 0.0.0.0:32768->80/tcp focused_bose

8、ENV（用于设置环境变量）

格式：

ENV  <value>
/<value>

例：

[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
#RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
#ENTRYPOINT ls /root /sys
#CMD ["-l"]
#ENTRYPOINT ["ls","/home"]
#RUN useradd admin
#USER admin
#EXPOSE 80
ENV a Hello World!!
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 2.048kB
Step 1/2 : FROM centos:latest
 ---> 9f38484d220f
Step 2/2 : ENV a Hello World!!
 ---> Running in af33c5e13754
Removing intermediate container af33c5e13754
 ---> dd22ab298385
Successfully built dd22ab298385
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test /bin/bash
[root@7dca23648303 /]# echo $a
Hello World!!

9、ADD（将源文件复制到container的目标文件）

格式：

ADD  <dest> 

/<dest>

注：src可以是Dockerfile所在目录的相对路径，也可以是一个绝对路径；

src为tar文件时，自动减压到dest中；

src为一个web的url时，会自动下载到dest中；

写dest路径时注意结尾的“/”，结尾有“/”和没“/”是有区别的

例：

[root@localhost docker]# pwd
/root/docker
[root@localhost docker]# echo "Hello World!!" > test.txt
[root@localhost docker]# wget http://nginx.org/download/nginx-1.16.1.tar.gz
[root@localhost docker]# ls
Dockerfile nginx-1.16.1.tar.gz test.txt
[root@localhost docker]# vim Dockerfile
#FROM centos
FROM centos:latest
#MAINTAINER Xuyun Liu <[email protected]>
#RUN touch /home/a.txt
#RUN ["touch","/home/b.txt"]
#CMD ls /dev
#CMD ["ls","/usr","/usr/local"]
#ENTRYPOINT ls /root /sys
#CMD ["-l"]
#ENTRYPOINT ["ls","/home"]
#RUN useradd admin
#USER admin
#EXPOSE 80
#ENV a Hello World!!
ADD test.txt /tmp
ADD nginx-1.16.1.tar.gz /tmp
ADD http://nginx.org/download/nginx-1.16.1.tar.gz /home
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 1.036MB
Step 1/4 : FROM centos:latest
 ---> 9f38484d220f
Step 2/4 : ADD test.txt /tmp 

 ---> 7fa385db5eef
Step 3/4 : ADD nginx-1.16.1.tar.gz /tmp
 ---> 24c9c0e0877d
Step 4/4 : ADD http://nginx.org/download/nginx-1.16.1.tar.gz /home
Downloading 1.033MB/1.033MB
 ---> b842677c7912
Successfully built b842677c7912
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test ls /tmp /home
/home:
nginx-1.16.1.tar.gz
/tmp:
ks-script-eC059Y nginx-1.16.1 test.txt yum.log #ks-script-eC059Y和yum.log是原有文件

10、COPY（复制本地主机的到容器中的<dest>，与ADD指令相似）/<dest>

格式：

COPY  <dest>
/<dest>

注：COPY指令和ADD指令功能和使用方式类似，但COPY指令只是复制，不会下载和解压

例：

[root@localhost docker]# echo "This is a test." > test.html
[root@localhost docker]# ls
Dockerfile nginx-1.16.1.tar.gz test.html test.txt
[root@localhost docker]# vim Dockerfile 
FROM centos:latest
COPY test.html /
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 1.037MB
Step 1/2 : FROM centos:latest
 ---> 9f38484d220f
Step 2/2 : COPY test.html /
 ---> e48a7c46ded6
Successfully built e48a7c46ded6
Successfully tagged my_test:latest 

[root@localhost docker]# docker run -it my_test ls -l /test.html
-rw-r--r-- 1 root root 16 Aug 29 18:30 /test.html

11、VOLUME（卷，指定挂载点）

格式：

VOLUME ["<mountpoint>"]
/<mountpoint>

12、WORKDIR（切换目录，可以多次切换，相当于cd命令）

格式：

WORKDIR Directory_url

例：

[root@localhost docker]# vim Dockerfile 
FROM centos:latest
WORKDIR /tmp
RUN mkdir test
WORKDIR test
RUN ["touch","a.txt","b.txt"]
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 1.037MB
Step 1/5 : FROM centos:latest
 ---> 9f38484d220f
Step 2/5 : WORKDIR /tmp
Removing intermediate container 9258f95093db
 ---> 6b8f6f6c69f6
Step 3/5 : RUN mkdir test
 ---> Running in e44f8d897714
Removing intermediate container e44f8d897714
 ---> 1dc77dd96431
Step 4/5 : WORKDIR test
Removing intermediate container df09ed12198d
 ---> 94cb324c6118
Step 5/5 : RUN ["touch","a.txt","b.txt"]
 ---> Running in 63f6bdcdd475
Removing intermediate container 63f6bdcdd475
 ---> 1ae6996b6573
Successfully built 1ae6996b6573
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test ls -l /tmp/test 

total 0
-rw-r--r-- 1 root root 0 Aug 29 18:39 a.txt
-rw-r--r-- 1 root root 0 Aug 29 18:39 b.txt

13、ONBUILD（在子镜像中执行）

格式：

ONBUILD INSTRUCTION

例：

[root@localhost docker]# vim Dockerfile 
[root@localhost docker]# docker build -t my_test .
Sending build context to Docker daemon 1.038MB
Step 1/2 : FROM centos:latest
 ---> 9f38484d220f
Step 2/2 : ONBUILD RUN touch /home/abc.txt
 ---> Running in b7f920c860a3
Removing intermediate container b7f920c860a3
 ---> 991234fb1d8e
Successfully built 991234fb1d8e
Successfully tagged my_test:latest
[root@localhost docker]# docker run -it my_test ls -l /home
total 0 #并没有创建abc.txt文件
[root@localhost docker]# mkdir test #需要再创建一个子Dockerfile文件，所以创建一个test目录来存放子Dockerfile文件，和父镜像的Dockerfile隔离开来
[root@localhost docker]# cd test
[root@localhost test]# pwd
/root/docker/test
[root@localhost test]# vim Dockerfile 
FROM my_test:latest #写父镜像
[root@localhost test]# docker build -t mytest2 .
Sending build context to Docker daemon 2.048kB
Step 1/1 : FROM my_test:latest
# Executing 1 build trigger
 ---> Running in b035d0948b03
Removing intermediate container b035d0948b03
 ---> 21e0f69c2eed
Successfully built 21e0f69c2eed
Successfully tagged mytest2:latest
[root@localhost test]# docker run -it mytest2 ls -l /home
total 0 

-rw-r--r-- 1 root root 0 Aug 29 18:58 abc.txt #此时会创建abc.txt文件

最后用两张张图解释常用指令的意义（有一说一图是从网上ba的，可能有点模糊不知道你们能不能看清，概括的挺好）