Alpine内存69m，安装docker: 内存120耗50m, caddy 约20m，
caddy：
apk add caddy
caddy start –config /etc/caddy/Caddyfile
caddy stop
apk add php7 #安装PHP7，我安装之后版本号 7.1.7
apk add mysql mysql-client #安装MySQL，实测安装成功后为 MariaDB 10.11.11-r0
/etc/init.d/mariadb setup
/etc/init.d/mariadb start