你用的应该是php的官方镜像为基础镜像吧, 他的redis安装是有个问题,你可以尝试这样解决
FROM php:7-fpm
RUN apt-get update \
&& apt-get install -y libmcrypt-dev mysql-client \
&& apt-get install -y zip unzip git \
&& apt-get install -y vim
RUN git clone -b php7 https://github.com/phpredis/phpredis.git /usr/src/php/ext/redis
RUN docker-php-ext-install mcrypt pdo_mysql session json mbstring redis
RUN curl -sS https://getcomposer.org/installer | php \
&& mv composer.phar /usr/local/bin/composer
WORKDIR /var/www