How to set hostname if hosting multiple servers on the same machine

domain-name-systemhostnamenetworkingsubdomainvirtualhost

I'm learning about setting up my own web and mail servers, and I've been confused about this question for days, and articles online (including Server Fault) seems to be so inconsistent with their use of the term 'subdomain' and 'hostname'.

From my understanding:

A host name uniquely identifies a computer in a network
A domain and subdomain must have a DNS A record which points to one or more hosts

Let's say my web server is at 1.2.3.4, I have my host name set to development (confirmed by running hostname in bash shell), and I'm setting A records like so:

@   -> 1.2.3.4
www -> 1.2.3.4
mx  -> 1.2.3.4
mx  -> 9.8.7.6

Then I have the www and mx subdomains pointing to my web server whose hostname is development. The mx subdoman also points to two hosts (for redundancy).

Why do I need a hostname? My machine can already be identified using its IP address.

I read somewhere that says a hostname is important because it gets sent in some messages. But if my server is both a mail server, and a file server, and a database server, and etc, what should I set my hostname to be? I certainly don't want someone receiving my mail to see a from address of development. And a machine can only have one hostname right? Should I set my computer's hostname to abc.example.com or just abc?

Main Question

How to set hostname if hosting multiple servers on the same machine?

Best Answer

The hostname is a convenience for uniquely identifying the host on your network. It's an entirely internal name that can be anything you want. The hostname doesn't have to be related to any of its DNS names.

For example, your host named abc can have DNS records that point to it as www.example.com, mail.example.com, and so on.

If you run local DNS within your LAN, you can also give your host a local DNS name of abc or abc.localdomain, so you can type http://abc into your browser. Again that just helps you to identify the host within your LAN.

Related Solutions

Hostname vs FQDN – Difference Between Hostname and Fully Qualified Domain Name

Your hostname is the name of your computer.

Your fully qualified domain name is your hostname plus the domain your company uses often ending in .local.

So if the name of your computer is bob, and your company's domain is contoso.local, your computer's fully qualified domain name (FQDN) is bob.contoso.local.:

Hostname: bob
Domain: contoso.com
FQDN: bob.contoso.com.

In the case of a domain like contoso.local I did not use an "external" internet domain name. This name doesn't have to be the only way that you address the server.
If you make it available by its IP address you can use DNS or that IP address to allow external users to access it.
The dot at the end of the FQDN is used to indicate the empty top-level domain.

Some more information on DNS:

Edit: Thanks for the comment on .local domains RobM

Setting the Hostname: FQDN or Short Name?

I would choose a consistent approach across the entire environment. Both solutions work fine and will remain compatible with most applications. There is a difference in manageability, though.

I go with the short name as the HOSTNAME setting, and set the FQDN as the first column in /etc/hosts for the server's IP, followed by the short name.

I have not encountered many software packages that enforce or display a preference between the two. I find the short name to be cleaner for some applications, specifically logging. Maybe I've been unlucky in seeing internal domains like server.northside.chicago.rizzomanufacturing.com. Who wants to see that in the logs or a shell prompt?

Sometimes, I'm involved in company acquisitions or restructuring where internal domains and/or subdomains change. I like using the short hostname in these cases because logging, kickstarts, printing, systems monitoring, etc. do not need full reconfiguration to account for the new domain names.

A typical RHEL/CentOS server setup for a server named "rizzo" with internal domain "ifp.com", would look like:

/etc/sysconfig/network:
HOSTNAME=rizzo
...

/etc/hosts:
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

172.16.100.13   rizzo.ifp.com rizzo

[root@rizzo ~]# hostname 
rizzo

/var/log/messages snippet:
Dec 15 10:10:13 rizzo proftpd[19675]: 172.16.100.13 (::ffff:206.15.236.182[::ffff:206.15.236.182]) - Preparing to               
 chroot to directory '/app/upload/GREEK'
Dec 15 10:10:51 rizzo proftpd[20660]: 172.16.100.13 (::ffff:12.28.170.2[::ffff:12.28.170.2]) - FTP session opened.
Dec 15 10:10:51 rizzo proftpd[20660]: 172.16.100.13 (::ffff:12.28.170.2[::ffff:12.28.170.2]) - Preparing to chroot                
to directory '/app/upload/ftp/SRRID'

Main Question

Best Answer

Related Solutions

Hostname vs FQDN – Difference Between Hostname and Fully Qualified Domain Name

Setting the Hostname: FQDN or Short Name?

Related Topic