Ensure your can visit real server through 80 port.please have a try.
If ok, you should check your dns about the domainName.
upstream webservers {
server xx.azurewebsites.netIP;
server xxx.azurewebsites.netIP;
}
server {
listen 80;
server_name localhost;
location / {
index index.html index.htm;
proxy_pass http://webservers;
proxy_set_header X-Real-IP $remote_addr;
}