Nginx configuration for redirect to a mobile version if mobile detected

redirect-if-mobile.conf

#-----------------------------
# alvinalexander.com (desktop)
#-----------------------------

server {
    server_name  alvinalexander.com;
    listen       80;

    #----- redirect to mobile check (starts) -----#
    set $mobile_rewrite do_not_perform;

    # this regex string is actually much longer to match more mobile devices
    if ($http_user_agent ~* "|android|ip(ad|hone|od)|kindle") {
        set $mobile_rewrite perform;
    }

    if ($mobile_rewrite = perform) {
        rewrite ^ http://m.alvinalexander.com$request_uri? redirect;
        break;
    }
    #----- redirect to mobile check (ends) -----#

    include /etc/nginx/aa-common.conf;

}

#------------------------------
# m.alvinalexander.com (mobile)
#------------------------------

server {
    server_name  m.alvinalexander.com;
    listen       80;
    include /etc/nginx/aa-common.conf;
}

# FROM: https://alvinalexander.com/technology/nginx-redirect-mobile-devices-users-mobile-website/