kubernetes里面有时候centos源用不了，快速配一个阿里云的源。
mkdir /etc/yum.repos.d/yangback;mv /etc/yum.repos.d/* /etc/yum.repos.d/yangback;curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo;yum clean all;yum repolist
/etc/yum.repos.d/yangback;mv /etc/yum.repos.d/* /etc/yum.repos.d/yangback;
/etc/yum.repos.d/