容器中安装composer

php -r "copy('https://install.phpcomposer.com/installer', 'composer-setup.php');"
php composer-setup.php

All settings correct for using Composer
Downloading...

Composer (version 1.6.5) successfully installed to: /root/composer.phar
Use it: php composer.phar
移动 composer.phar，这样 composer 就可以进行全局调用：

mv composer.phar /usr/local/bin/composer

切换为国内镜像：

composer config -g repo.packagist composer https://packagist.phpcomposer.com

更新 composer：

composer selfupdate