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.