dockerfile指令说明

• 第一条指令必须指定基础镜像
  FROM imageA:tag

• RUN 指定运行的命令
  一般是基于基础容器，搭建基础环境的操作，属于build image的时候操作的；使用RUN指令的时候，最好不要写多层RUN，使用下面一种形式，\分隔换行继续写就行了，不然层级增加，不利于镜像可读性和简约性
  RUN direct-command
RUN ["executed-file","param1","param2"]

• CMD 指令只出容器启动时需要的命令
  与RUN指令的使用实际不同；这里使用可执行文件传参数的时候，要注意使用双引号，参数传递以后，docker会解析成json串
  CMD ["executed-file","param1","param2"]
CMD direct-command parames

• LABEL 添加镜像标签
  LABEL key=value key2=value2

• MAINTAINER指定作者
  MAINTAINER author

• EXPOSE 对外端口
  EXPOSE端口指定的是外部访问该容器的端口，与主机端口无关，如需要添加映射关系，使用-P参数
  EXPOSE 7171

• 设置环境变量
  ENV key=value key2=value2

• ADD 添加文件到镜像中
  可以使用容器内的绝对路径，也可以使用相对路径；file的格式原则上是不限制的，使用过程中可以根据实际情况评估
  ADD filename/url path

• COPY 拷贝文件
  COPY filename path

• ENTERPOINT
  启动时的默认命令，用法与RUN和CMD一样
  如果同时写了ENTERPOINT和CMD，二者可能会相互覆盖，，？

• VOLUME挂载
  一般多设置于需要持久化存储

• USER容器启动用户
  指定运行命令的层，执行命令的身份
  USER user_name

• WORKDIR 工作目录
  如果不存在会创建；存在以后多设置几次也ok
  WORKDIR path

• ARG设置变量

• ONBUILD 基于当前镜像生成的子镜像才会有的动作
  例如 ONBUILD CMD direct-command parames 这种

• STOPSIGNAL 容器退出时的系统指令

• HEALTHCHECK 健康检查

>> 示例<<

FROM centos:7.1
MAINTAINER M_G
LABEL im_name="my_centos7"\
      im_desc="centos7.1byM_G"\
      im_version="1.0"
RUN /bin/echo "Testing-RUN1"\
    /bin/echo "Testing-RUN2"\
    /bin/echo "Testing-RUN3"\
    /bin/echo "The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile"
RUN ["/bin/echo", "-c", "OtherMeth"]
EXPOSE 7788
CMD /bin/echo "CMD"

>> 示例运行结果 <<

docker build -t runtest/centos:7.1 .
Sending build context to Docker daemon  2.048kB
Step 1/7 : FROM centos:7.2.1511
 ---> 9aec5c5fe4ba
Step 2/7 : MAINTAINER M_G
 ---> Running in fd9773ab5d04
Removing intermediate container fd9773ab5d04
 ---> 5d049cf44ade
Step 3/7 : LABEL im_name="my_centos7"      im_desc="centos7.1byM_G"   im_version="1.0"
 ---> Running in dbe78be6937a
Removing intermediate container dbe78be6937a
 ---> 835de35557c0
Step 4/7 : RUN /bin/echo "Testing-RUN1" /bin/echo "Testing-RUN2"    /bin/echo "Testing-RUN3"    /bin/echo "The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile"
 ---> Running in 200e155ce261
Testing-RUN1 /bin/echo Testing-RUN2 /bin/echo Testing-RUN3 /bin/echo The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile
Removing intermediate container 200e155ce261
 ---> 6b20860bc949
Step 5/7 : RUN ["/bin/echo", "-c", "OtherMeth"]
 ---> Running in 39064900f238
-c OtherMeth
Removing intermediate container 39064900f238
 ---> 47e32cba5448
Step 6/7 : EXPOSE 7788
 ---> Running in c658c7ba76ea
Removing intermediate container c658c7ba76ea
 ---> e76255a7950f
Step 7/7 : CMD /bin/echo "CMD"
 ---> Running in 9ab1ff69c36d
Removing intermediate container 9ab1ff69c36d
 ---> 91f66f06b528
Successfully built 91f66f06b528
Successfully tagged runtest/centos:7.1

完成以上指令，docker images已经创建成功，测试一下：

docker run -t -i runtest/centos:7.1 /bin/echo "TEST"
# output
TEST