基本結構

Dockerfile 由一行行命令語句組成，並且支援以 # 開頭的註解行。一般而言，Dockerfile 分為四部分：基底映像檔資訊、維護者資訊、映像檔操作指令和容器啟動時執行指令。例如：

# This dockerfile uses the ubuntu image
# VERSION 2 - EDITION 1
# Author: docker_user
# Command format: Instruction [arguments / command] ..

# 基本映像檔，必須是第一個指令
FROM ubuntu

# 維護者： docker_user <docker_user at email.com> (@docker_user)
MAINTAINER docker_user [e-mail]

# 更新映像檔的指令
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

# 建立新容器時要執行的指令
CMD /usr/sbin/nginx

其中，一開始必須指明作為基底的映像檔名稱，接下來說明維護者資訊（建議）。接著則是映像檔操作指令，例如 RUN 指令，RUN 指令將對映像檔執行相對應的命令。每運行一條 RUN 指令，映像檔就會新增一層。最後是 CMD 指令，指定執行容器時的操作命令。下面來看一個更複雜的例子：

# Nginx
#
# VERSION               0.0.1

FROM      ubuntu
MAINTAINER Victor Vieux <[e-mail]>

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.