Is it possible to use the same domain name for all servers?
Yes, but (arguably) this doesn't appear to be what you are asking about. That is, it is possible to have a single domain (e.g.
example.com) that is serviced by multiple (duplicated) servers.
What you appear to be asking about are subdomains. In short, it is possible to assign separate IPs to separate subdomains in DNS, so that subdomains
s3.example.com etc. are all serviced by different servers (IP addresses). You simply need an e.g. A record for each subdomain.
What should I put in the host field?
You don't specify what DNS setup you are using, but typically this would be the subdomain (e.g.
There is an @ symbol for the main domain.
At least in BIND, the
@ symbol is a shorthand way of referencing the
zone root or
zone apex (often e.g.
example.com). This entry is generally necessary. You would add additional A records for each subdomain.