docker官方鏡像為安裝php擴展封裝了函數，為開發者提供了很大的便利，以下以Dockerfile的形式演示安裝gd擴展的方法，安裝gd擴展需要安裝幾個依賴包，安裝依賴包使用系統命令，安裝命令根據基礎鏡像的不同有所不同，以下演示兩種使用較多的alpine和debian系統的Dockerfile，Dockerfile中同時包含更換國內開源鏡像源的內容。
1、基礎鏡像 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$(nproc) gd
EXPOSE 9000
CMD ["php-fpm"]
2、基礎鏡像 php:7.2-fpm-stretch （debian 9）
Dockerfile如下：
FROM php:7.2-fpm-stretch
RUN echo "deb http://mirrors.aliyun.com/debian/ stretch main non-free contrib" > /etc/apt/sources.list \
&& echo "deb-src http://mirrors.aliyun.com/debian/ stretch main non-free contrib" >> /etc/apt/sources.list \
&& echo "deb http://mirrors.aliyun.com/debian-security stretch/updates main" >> /etc/apt/sources.list \
&& echo "deb-src http://mirrors.aliyun.com/debian-security stretch/updates main" >> /etc/apt/sources.list \
&& echo "deb http://mirrors.aliyun.com/debian/ stretch-updates main non-free contrib" >> /etc/apt/sources.list \
&& echo "deb-src http://mirrors.aliyun.com/debian/ stretch-updates main non-free contrib" >> /etc/apt/sources.list \
&& echo "deb http://mirrors.aliyun.com/debian/ stretch-backports main non-free contrib" >> /etc/apt/sources.list \
&& echo "deb-src http://mirrors.aliyun.com/debian/ stretch-backports main non-free contrib" >> /etc/apt/sources.list \
&& rm -f /etc/apt/sources.list.d/* \
&& apt-get update && apt-get install -y \
libfreetype6-dev \
libjpeg62-turbo-dev \
libpng-dev \
&& docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ --with-png-dir=/usr/include \
&& docker-php-ext-install -j$(nproc) gd
EXPOSE 9000
CMD ["php-fpm"]