Add dockerfile chapter

dockerfile/basic_structure.md

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+## 基本结构
+Dockerfile由一行行命令语句组成，并且支持以`#`开头的注释行。
+
+一般的，Dockerfile分为四部分：基础镜像信息、维护者信息、镜像操作指令和容器启动时执行指令。
+
+例如
+```
+# This dockerfile uses the ubuntu image
+# VERSION 2 - EDITION 1
+# Author: docker_user
+# Command format: Instruction [arguments / command] ..
+
+# Base image to use, this must be set as the first line
+FROM ubuntu
+
+# Maintainer: docker_user <docker_user at email.com> (@docker_user)
+MAINTAINER docker_user docker_user@email.com
+
+# Commands to update the image
+RUN echo "deb http://archive.ubuntu.com/ubuntu/ raring main universe" >> /etc/apt/sources.list
+RUN apt-get update && apt-get install -y nginx
+RUN echo "\ndaemon off;" >> /etc/nginx/nginx.conf
+
+# Commands when creating a new container
+CMD /usr/sbin/nginx
+```
+
+其中，一开始必须指明所基于的镜像名称，接下来推荐说明维护者信息。
+
+后面则是镜像操作指令，例如`RUN`指令，`RUN`指令将对镜像执行跟随的命令。每运行一条`RUN`指令，镜像添加新的一层，并提交。
+
+最后是`CMD`指令，来指定运行容器时的操作命令。
+
+下面是一个更复杂的例子
+```
+# Nginx
+#
+# VERSION               0.0.1
+
+FROM      ubuntu
+MAINTAINER Victor Vieux <victor@docker.com>
+
+RUN apt-get update && apt-get install -y inotify-tools nginx apache2 openssh-server
+
+# Firefox over VNC
+#
+# VERSION               0.3
+
+FROM ubuntu
+
+# Install vnc, xvfb in order to create a 'fake' display and firefox
+RUN apt-get update && apt-get install -y x11vnc xvfb firefox
+RUN mkdir /.vnc
+# Setup a password
+RUN x11vnc -storepasswd 1234 ~/.vnc/passwd
+# Autostart firefox (might not be the best way, but it does the trick)
+RUN bash -c 'echo "firefox" >> /.bashrc'
+
+EXPOSE 5900
+CMD    ["x11vnc", "-forever", "-usepw", "-create"]
+
+# Multiple images example
+#
+# VERSION               0.1
+
+FROM ubuntu
+RUN echo foo > bar
+# Will output something like ===> 907ad6c2736f
+
+FROM ubuntu
+RUN echo moo > oink
+# Will output something like ===> 695d7793cbe4
+
+# You᾿ll now have two images, 907ad6c2736f with /bar, and 695d7793cbe4 with
+# /oink.
+```