docker笔记之Dockerfile体系结构

Dockerfile体系结构（保留字指令）

FROM：基础镜像，当前镜像是基于哪个镜像的
MAINTAINER：镜像维护者的姓名和邮箱地址
RUN：容器构件时需要运行的命令
EXPOSE：当前容器对外暴露出的端口
WORKDIR：指定在创建容器后，终端默认登陆进来的工作目录
ENV：用来在构建镜像过程中设置环境变量
ADD：将宿主机目录下的文件拷贝进镜像且ADD命令会自动处理URL和解压tar压缩包
COPY：类似ADD，拷贝文件和目录到镜像中。将从构建上下文目录中<源路径>的文件/目录复制到新的一层的镜像内的<目标路径>位置
VOLUME：容器数据卷，用于数据保存和持久化工作
CMD：指定一个容器启动时要执行的命令，dockerfile中可以存在多个CMD，但是只有最后一个生效，前面会被覆盖
ENTRYPOINT：指定一个容器启动时要执行的命令，和CMD一样，都是在指定容器启动程序和参数
ONBUILD：当构建一个被继承的Dockerfile时运行命令，父镜像在被子镜像继承后父镜像的onbuild被触发

示例

01根据centos的官方镜像创建一个查询自己出口IP的容器

[root@heibing 20190911]# cat Dockerfile 
FROM centos
RUN yum install curl -y
CMD ["curl","-s","https://ip.cn/"]
[root@heibing 20190911]# docker build -f Dockerfile -t myip .
Sending build context to Docker daemon  2.048kB
Step 1/3 : FROM centos
 ---> 67fa590cfc1c
Step 2/3 : RUN yum install curl -y
 ---> Running in fe556a2f7dd5
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
 * base: mirror.jdcloud.com
 * extras: mirrors.huaweicloud.com
 * updates: mirror.jdcloud.com
Package curl-7.29.0-51.el7_6.3.x86_64 already installed and latest version
Nothing to do
Removing intermediate container fe556a2f7dd5
 ---> 308ad7c5bc9d
Step 3/3 : CMD ["curl","-s","https://ip.cn/"]
 ---> Running in e3fb5e4ea34e
Removing intermediate container e3fb5e4ea34e
 ---> 71438add7273
Successfully built 71438add7273
Successfully tagged myip:latest
[root@heibing 20190911]# docker run -it myip
{"ip": "223.71.81.68", "country": "北京市", "city": "移动"}

#CMD覆盖问题
[root@heibing 20190911]# docker run -it myip ls -l
total 56
-rw-r--r--.  1 root root 12090 Aug  1 01:10 anaconda-post.log
lrwxrwxrwx.  1 root root     7 Aug  1 01:09 bin -> usr/bin
drwxr-xr-x.  5 root root   360 Sep 11 17:18 dev
drwxr-xr-x.  1 root root  4096 Sep 11 17:18 etc
#从这里可以看出，CMD命令可以被run后面的参数覆盖，导致预设的命令失效

02将test.txt拷贝至镜像中，并在启动容器时输出文件内容

[root@heibing 20190911]# cat Dockerfile1
FROM centos
RUN yum install curl -y
COPY test.txt /tmp/
CMD ["cat","/tmp/test.txt"]
[root@heibing 20190911]# cat test.txt 
Hello,World~~
[root@heibing 20190911]# docker build -f Dockerfile1 -t my_test .
Sending build context to Docker daemon  4.096kB
Step 1/4 : FROM centos
 ---> 67fa590cfc1c
Step 2/4 : RUN yum install curl -y
 ---> Using cache
 ---> 308ad7c5bc9d
Step 3/4 : COPY test.txt /tmp/
 ---> Using cache
 ---> dd18f6d40c2f
Step 4/4 : CMD ["cat","/tmp/test.txt"]
 ---> Running in c3e9867de724
Removing intermediate container c3e9867de724
 ---> d934ab117265
Successfully built d934ab117265
Successfully tagged my_test:latest
[root@heibing 20190911]# docker run -it my_test
Hello,World~~

03通过ADD命令将压缩包内容拷贝至镜像中

#通过for循环生成10个文件
[root@heibing 20190911]# for i in `seq 10`;do touch $i.txt;done
[root@heibing 20190911]# ls
1,10.txt  1.txt  10.txt  2.txt  3.txt  4.txt  5.txt  6.txt  7.txt  8.txt  9.txt  Dockerfile  Dockerfile1  test.txt
#将文件打包
[root@heibing 20190911]# tar zcvf test.tar.gz ./*.txt
./1,10.txt
./1.txt
./10.txt
./2.txt
./3.txt
./4.txt
./5.txt
./6.txt
./7.txt
./8.txt
./9.txt
./test.txt
[root@heibing 20190911]# ls
1,10.txt  1.txt  10.txt  2.txt  3.txt  4.txt  5.txt  6.txt  7.txt  8.txt  9.txt  Dockerfile  Dockerfile1  test.tar.gz  test.txt
#编写Dockerfile文件
[root@heibing 20190911]# cat Dockerfile2
FROM centos
ADD test.tar.gz /tmp/
CMD ["ls","/tmp"]
#生成镜像
[root@heibing 20190911]# docker build -f Dockerfile2 -t my_test .
Sending build context to Docker daemon   12.8kB
Step 1/3 : FROM centos
 ---> 67fa590cfc1c
Step 2/3 : ADD test.tar.gz /tmp/
 ---> a38cc88f9d06
Step 3/3 : CMD ["ls","/tmp"]
 ---> Running in 38d615919937
Removing intermediate container 38d615919937
 ---> 0b1fc9cc784f
Successfully built 0b1fc9cc784f
Successfully tagged my_test:latest
#启动容器查看结果
[root@heibing 20190911]# docker run -it my_test
1,10.txt  10.txt  3.txt  5.txt	7.txt  9.txt		 test.txt
1.txt	  2.txt   4.txt  6.txt	8.txt  ks-script-rnBCJB  yum.log