docker官方镜像为安装php扩展封装了函数，为开发者提供了很大的便利，以下以Dockerfile的形式演示安装gd扩展的方法，安装gd扩展需要安装几个依赖包，安装依赖包使用系统命令，安装命令根据基础镜像的不同有所不同，以下演示两种使用较多的alpine和debian系统的Dockerfile，Dockerfile中同时包含更换国内开源镜像源的内容。
1、基础镜像 php:7.2-fpm-alpine
Dockerfile如下：
FROM php:7.2-fpm-alpine
RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
&& apk update
&& apk add libpng-dev freetype-dev libjpeg-turbo-dev
&& docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ --with-png-dir=/usr/include/
&& docker-php-ext-install -j$(nproc) gd
EXPOSE 9000
CMD ["php-fpm"]
2、基础镜像 php:7.2-fpm-stretch （debian 9）
Dockerfile如下：
FROM php:7.2-fpm-stretch
RUN echo "deb http://mirrors.aliyun.com/debian/ stretch main non-free contrib" > /etc/apt/sources.list
&& echo "deb-src http://mirrors.aliyun.com/debian/ stretch main non-free contrib" >> /etc/apt/sources.list
&& echo "deb http://mirrors.aliyun.com/debian-security stretch/updates main" >> /etc/apt/sources.list
&& echo "deb-src http://mirrors.aliyun.com/debian-security stretch/updates main" >> /etc/apt/sources.list
&& echo "deb http://mirrors.aliyun.com/debian/ stretch-updates main non-free contrib" >> /etc/apt/sources.list
&& echo "deb-src http://mirrors.aliyun.com/debian/ stretch-updates main non-free contrib" >> /etc/apt/sources.list
&& echo "deb http://mirrors.aliyun.com/debian/ stretch-backports main non-free contrib" >> /etc/apt/sources.list
&& echo "deb-src http://mirrors.aliyun.com/debian/ stretch-backports main non-free contrib" >> /etc/apt/sources.list
&& rm -f /etc/apt/sources.list.d/*
&& apt-get update && apt-get install -y
libfreetype6-dev
libjpeg62-turbo-dev
libpng-dev
&& docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ --with-png-dir=/usr/include
&& docker-php-ext-install -j$(nproc) gd
EXPOSE 9000
CMD ["php-fpm"]