安装 GD 扩展时需要额外的依赖和配置，但是官方文档中只给出了 Debian 系的解决方案。通过查阅网络资料，得到了 Alpine 下的解决方案，写成 Dockerfile 如下：

FROM php:7.3.2-fpm-alpine
RUN apk add \
        freetype \
        freetype-dev \
        libpng \
        libpng-dev \
        libjpeg-turbo \
        libjpeg-turbo-dev \
    && docker-php-ext-configure gd \
        --with-freetype-dir=/usr/include/ \
        --with-jpeg-dir=/usr/include/ \
    && docker-php-ext-install -j$(nproc) gd \
    && apk del \
        freetype-dev \
        libpng-dev \
        libjpeg-turbo-dev \
    && rm /var/cache/apk/*

还有找到的

FROM php:5.6-fpm-alpine
ENV TIMEZONE Asia/Shanghai
ENV PHP_MEMORY_LIMIT 512M
ENV MAX_UPLOAD 50M
ENV PHP_MAX_FILE_UPLOAD 200
ENV PHP_MAX_POST 100M
ADD ./redis /usr/src/php/ext/redis
RUN apk --update add tzdata \
   libjpeg-turbo-dev \
     libpng-dev \
   freetype-dev \
  && cp /usr/share/zoneinfo/${TIMEZONE} /etc/localtime \
  && echo "${TIMEZONE}" > /etc/timezone
RUN docker-php-ext-configure gd --with-freetype-dir=/usr/include/freetype2 --with-png-dir=/usr --enable-gd-native-ttf --with-jpeg-dir=/usr \
    && docker-php-ext-install redis mysqli gd pdo_mysql redis opcache zip 
RUN mkdir /www \
  && apk del tzdata curl \
  && rm -rf /var/cache/apk/*