docker_practice/dockerfile/basic_structure.md

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## 基本結構
Dockerfile 由一行行命令語句組成,並且支援以 `#` 開頭的注釋行。
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一般而言Dockerfile 分為四部分:基礎鏡像資訊、維護者資訊、鏡像操作指令和容器啟動時執行指令。
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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,一開始必須指明所基於的鏡像名稱,接下來建議說明維護者資訊。
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後面則是鏡像操作指令,例如 `RUN` 指令,`RUN` 指令將對鏡像執行伴隨的命令。每運行一條 `RUN` 指令,鏡像添加新的一層,並提交。
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最後是 `CMD` 指令,來指定運行容器時的操作命令。
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下面來看一個更複雜的例子
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```
# 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.
```