https://mirrors.aliyun.com/
 
https://mirrors.aliyun.com/epel/7/x86_64/
 
http://mirrors.aliyun.com/repo/

OpenStack源：
centos：http://mirror.centos.org/centos/7/cloud/x86_64/
北理工：http://mirror.bit.edu.cn/centos/7/cloud/x86_64/
阿里云：http://mirrors.aliyun.com/centos/7/cloud/x86_64/

第一步：备份

mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup

第二步：下载repo文件

wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

第三步：将/etc/yum.repos.d/CentOS-Base.repo，里面的http都改成https

sed  -i 's/http/https/g'  /etc/yum.repos.d/CentOS-Base.repo

第四步：执行yum源更新命令

yum clean all
yum makecache
yum update