Hello!
I,we got 2 servers: one should be gateway and another is a hosting server for some services like web, email, ftp, dns etc.
The thing is every domain is bind on its own ip address.
Lets say, i have 3 internet ip addresses:
domain1: 108.144.4.350
domain2: 108.144.4.351
domain3: 108.144.4.352

I should place all my services behind gateway, separately. I mean every domain is available only on its own ip address.

Thats what i think: On my gateway i place HAProxy to proxying http and https(maybe in the future i'd have to balance traffic) and then im SNAT and DNAT forward:
iptables -A PREROUTING -i eth1 -p 0 -m 0 -o eth0 -d 108.144.4.350 -j DNAT --to-destination 10.10.10.2

10.10.10.2 - is equivalent for domain1, which was 108.144.4.350.

Any suggestions?
Thank you very much!

Domain concept is different from service normally. You can treat them as same if you like.
My point is that you can use different IP if you talk about domain. But for service, you can use different well-known port instead of IP.