写在前面

Dockerfile是用来构建镜像的，他实际上就是把在linux下的命令操作写到了Dockerfile中，通过Dockerfile去执行设置好的操作命令，保证通过Dockerfile的构建镜像是一致的。

实战分析

该例子来自于 chromium 项目
主要干的事情：

1. 来指定用哪个镜像；
2. 安装一些编译需要的环境：C++编译环境，Java环境等

# This Dockerfile specifies the recipe for creating an image for the tests
# to run in.
#
# We install as many test dependencies here as we can, because these setup
# steps can be cached.  They do *not* run every time we run the build.
# The Docker image is only rebuilt when the Dockerfile (ie. this file)
# changes.# 指定了使用什么镜像 debian
# Base Dockerfile for gRPC dev images
FROM debian:latest# 添加软件源
# Apt source for old Python versions.
RUN echo 'deb http://ppa.launchpad.net/fkrull/deadsnakes/ubuntu trusty main' > /etc/apt/sources.list.d/deadsnakes.list && \apt-key adv --keyserver keyserver.ubuntu.com --recv-keys DB82666C# Apt source for Oracle Java.
RUN echo 'deb http://ppa.launchpad.net/webupd8team/java/ubuntu trusty main' > /etc/apt/sources.list.d/webupd8team-java-trusty.list && \apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EEA14886 && \echo "oracle-java7-installer shared/accepted-oracle-license-v1-1 select true" | debconf-set-selections# Apt source for Mono
RUN echo "deb http://download.mono-project.com/repo/debian wheezy main" | tee /etc/apt/sources.list.d/mono-xamarin.list && \echo "deb http://download.mono-project.com/repo/debian wheezy-libjpeg62-compat main" | tee -a /etc/apt/sources.list.d/mono-xamarin.list && \apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF# Apt source for php
RUN echo "deb http://ppa.launchpad.net/ondrej/php/ubuntu trusty main" | tee /etc/apt/sources.list.d/various-php.list && \apt-key adv --keyserver keyserver.ubuntu.com --recv-keys F4FCBB07# Install dotnet SDK based on https://www.microsoft.com/net/core#debian
# (Ubuntu instructions need apt to support https)
RUN apt-get update && apt-get install -y --force-yes curl libunwind8 gettext && \curl -sSL -o dotnet.tar.gz https://go.microsoft.com/fwlink/?LinkID=847105 &&  \mkdir -p /opt/dotnet && tar zxf dotnet.tar.gz -C /opt/dotnet && \ln -s /opt/dotnet/dotnet /usr/local/bin# Install dependencies.  We start with the basic ones require to build protoc
# and the C++ build
RUN apt-get clean && apt-get update && apt-get install -y --force-yes \autoconf \autotools-dev \build-essential \bzip2 \ccache \curl \gcc \git \libc6 \libc6-dbg \libc6-dev \libgtest-dev \libtool \make \parallel \time \wget \# -- For csharp --mono-devel \referenceassemblies-pcl \nunit \# -- For all Java builds -- \maven \# -- For java_jdk6 -- \#   oops! not in jessie. too old? openjdk-6-jdk \# -- For java_jdk7 -- \openjdk-7-jdk \# -- For java_oracle7 -- \oracle-java7-installer \# -- For python / python_cpp -- \python-setuptools \python-pip \python-dev \python2.6-dev \python3.3-dev \python3.4-dev \# -- For Ruby --ruby \# -- For C++ benchmarks --cmake \# -- For PHP --php5.6     \php5.6-dev \php5.6-xml \php7.0     \ph