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. |
