起因：启动了Amazon Linux 2 无法 yum install nginx

# 解决办法
yum install -y amazon-linux-extras
amazon-linux-extras list | grep nginx
amazon-linux-extras install nginx1
systemctl enable nginx
systemctl start nginx

引用：https://aws.amazon.com/cn/premiumsupport/knowledge-center/ec2-install-extras-library-software/