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为什么要使用Dockerfile
Dockerfile 能搭建出一抹一样的环境来,而且操作方便，简单，环境一致
注：base p_w_picpaths需统一， 可以从灵鹊云，数字云，阿里云中直接pull。直接在官方dockerhub中pull实在是太慢了，还经常失败
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Dockerfile 语法如下，跟我们熟悉的shell一样，是顺序向下执行的。
Dockerfile 执行与注意点
docker build . docker build -t centos:7 . docker build -t centos:7 -t centos:latest . docker build -f /path/docker/file/Dockerfile .
tips：
1. 整个build过程是由Docker daemon 控制的，并非CLI 2. Dockerfile 尽量别放到node的 '/' 目录下，否则会将整个根目录全部send到docker daemon 3. Docker build 过程中每一行是独立的(有点类似Makefile),所如果前面定义RUN cd /tmp ，后面定义 RUN touch file ，这个file一定不会在/tmp下面
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Environment replacement
Dockerfile 中的变量是有ENV定义。变量比较有意思，有好多中写法，大家研究一下看：
1. $foo , ${foo}
3. \$foo ,\${foo}
4. ${fool_name} ,$fool_name, ${fool}_cont
5. ${variable:-word} , 如果$variable 没有设置，那么传递的值就是word
6. ${variable:+word} ，如果$variable 已经设置，那么传递的值就是word并非所有的Dockerfile指令都能support ENV ，我们看看有哪些能够support:
ADD,COPY,ENV，EXPOSE,LABEL,USER,WORKDIR,VOLUME,STOPSIGNAL
目前就只有这么多了
注：在Dockerfile同一行中ENV环境变量是保持不替换的，什么意思呢？我们看个例子就很清楚了。
ENV abc=hello ENV abc=bye def=$abc ENV ghi=$abc
结果 def=hello， ghi=bye，
因为在第二个ENV中，abc变量虽然是有被重新赋值，但是因为跟def赋值是在同一行，所以了结果就是依然是上一行的值，是不是很有趣:)
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#Comment
#INSTRUCTION arguments
FROM <p_w_picpaths:tag> ex: FROM centos:6.6
如果没有对应的p_w_picpaths，那么会直接从公共的dockerhub中pull（当然直接dockerhub的server就是另外一回事了）
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MAINTANER <name>
ex: MAINTAINER GuiQiu<guiqiu_2010@162.com>
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RUN <command>
两种模式，一种是shell模式，这种模式等于说是/bin/sh -c command这样执行
ex： RUN echo "$NAME is my friend" RUN yum install -y mysql \ python RUN /bin/bash -c 'source $HOME/.bashrc ;\ echo $HOME'
另一种模式，exec模式 ,因为这种模式将option当作JSON array来parser的，所以一定是要使用双引号的。
RUN ["executable", "param1", "param2"] ex： RUN ["/bin/bash", "-c", "echo hello"] RUN [ "echo", "$HOME" ]
在exec模式中，如果有变量，那么在parser的时候，是不传值的，要记得。
tips：在测试阶段，Dockerfile一直频繁的修改，所以我们在build的时候，有时候不希望使用上一版或上几版的cache，可以使用下面的命令避免(个人感觉还蛮有作用的)
docker build --no-cache
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CMD ["executable","param1","param2"] (exec form, this is the preferred form) CMD ["param1","param2"] (as default parameters to ENTRYPOINT) CMD command param1 param2 (shell form)
ENTRYPOINT ["executable", "param1", "param2"] (exec form, preferred) ENTRYPOINT command param1 param2 (shell form)
用此option可以避免使用Dockerfile中定义的ENTRYPOINT值：--entrypoint=flag
tips:
1. 如果CMD 是给ENTRYPOINT 提供参数的话，那么必须使用JSON格式，也就是必须要双引号(不是单引号)
2. ENTRYPOINT CMD 区别是 ENTRYPOINT的指令不会被user指定的命令overwrite，而是当作参数使用；CMD定义的指令会直接被overwrite
3. CMD RUN 的区别，RUN指令会在build过程中指令且commit，然而CMD 却只是定义到p_w_picpaths中，不会在build的过程中执行，只是在container启动的时候执行
4. 当container别当成一个执行档来用的时候，比较难建议使用ENTRYPOINT + CMD 执行一些参数
5. Dockerfile 必须定义ENTRYPOINT CMD其中之一
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ADD/COPY ADD <src>... <dest> ADD ["<src>",... "<dest>"] COPY <src>... <dest> COPY ["<src>",... "<dest>"]
tips：
1. ADD / COPY 都是复制的作用，但是ADD 可以直接复制url而COPY则需要先download下来然后才能复制，当然如果url中有需要密码认证的话，还是必须通过其他的方式来先得到内容才能复制
2. src的路径必须包含在Dockerfile所在的路径下
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USER daemon
以什么user来运行此container
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WORKDIR path
container 开启之后default路径
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[root@guiqiu-virtualbox dockerfile]# cat Dockerfile FROM centos:test MAINTAINER GUIQIU<guiqiu_2010@163.com> ENV FILENAME DOCKERFILE ENV MYNAME=zhangsan YOURNAME=lisi RUN yum install -y xclock RUN yum install -y openssh-server \ openssh-clients RUN ["mkdir", "-p" ,"/d/test"] RUN useradd zhangsan ADD README /root/ COPY README /d/test WORKDIR /d USER zhangsan CMD /bin/bash
[root@guiqiu-virtualbox dockerfile]# cat Dockerfile1 FROM centos:test MAINTAINER GUIQIU<guiqiu_2010@163.com> ENV FILENAME DOCKERFILE ENV MYNAME=zhangsan YOURNAME=lisi RUN yum install -y xclock RUN yum install -y perl \ openssh-server \ openssh-clients RUN ["mkdir", "-p" ,"/d/test"] ADD README /root/ COPY README /d/test WORKDIR /d CMD /bin/bash
[root@guiqiu-virtualbox dockerfile]# cat Dockerfile2 FROM centos:test MAINTAINER GUIQIU<guiqiu_2010@163.com> ENV FILENAME DOCKERFILE ENV MYNAME=zhangsan YOURNAME=lisi RUN yum install -y xclock RUN yum install -y perl \ openssh-server \ openssh-clients RUN ["mkdir", "-p" ,"/d/test"] ADD README /root/ COPY README /d/test WORKDIR /d ENTRYPOINT ["/bin/bash"]
[root@guiqiu-virtualbox dockerfile]# cat Dockerfile3 FROM centos:test MAINTAINER GUIQIU<guiqiu_2010@163.com> ENV FILENAME DOCKERFILE ENV MYNAME=zhangsan YOURNAME=lisi RUN yum install -y xclock RUN yum install -y perl \ openssh-server \ openssh-clients RUN ["mkdir", "-p" ,"/d/test"] ADD README /root/ COPY README /d/test WORKDIR /d ENTRYPOINT ["/usr/bin/echo","ThisIsTest"]
