based on the default file, combined with your section, the file now looks like this:

worker_processes 1;

events {
worker_connections 1024;
}


http {
include mime.types;
default_type application/octet-stream;
sendfile on;
keepalive_timeout 65;

server {
server_name gw.mydomain.com;
location / {
proxy_pass http://192.168.XX.5;
}
}

server {
server_name cloud.mydomain.com;
location / {
proxy_pass http://192.168.XX.6;
}
}
}


(domain name and IP changed).

However, NGINX does not start:

[root@ipfire nginx]# /etc/init.d/nginx restart
Stopping nginx Server... [ OK ]
Starting nginx Server...
nginx: [emerg] could not build server_names_hash, you should increase server_names_hash_bucket_size: 32