ngx_http_rewrite_module模块：将用户请求的URI基于PCRE regex所描述的模式进行检查，而后完成重定向替换

一、使用if判断，通过return，将http跳转到https

vim /etc/nginx/conf.d/test.conf
server {
        listen 443 ssl;
        listen 80;
        server_name www.a.net;
        root /data/site1/;
        ssl_certificate /etc/nginx/ssl/www.a.net.crt;
        ssl_certificate_key /etc/nginx/ssl/www.a.net.key;
        ssl_session_cache shared:sslcache:20m;
        ssl_session_timeout 10m;
        access_log /var/log/nginx/a.net.log443 main;
        location / {
            if ( $scheme = http ){
                return 301 https://www.a.net/;
                }
        }

}