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The 
/etc/hosts
 file, which we briefly discussed while working with our hostname, 
tells our server how to resolve itself (it has a hostname mapping to the localhost IP 
of 
127.0.0.1
), but you are also able to create additional names to IP mappings here 
as well. For example, if I had a server (
myserver.mydomain.org
) at IP 
10.10.96.124
, I 
could add the following line to 
/etc/hosts
 to make my machine resolve the server to 
that IP each time, without it needing to consult a DNS server at all:
10.10.96.124 myserver.mydomain.org 
In practice though, this is usually not a very convenient method by which to 
configure name resolution. Don't get me wrong, you can certainly list your servers 
in this file along with their IP addresses, and your server would be able to resolve 
those names just fine. The problem stems from the fact that this method is difficult to 
maintain. The name mappings apply only to the server you've made the 
/etc/hosts
 
changes on; other servers wouldn't benefit since they would only check their own 
/etc/hosts
 file. You could add a list of servers to the hosts file on each of your 
servers, but that would be a pain to manage. This is the main reason why having a 
central DNS server is a benefit to any network, especially for resolving the names of 
local resources.
However, the 
/etc/hosts
 file is used every now and again in the enterprise as a 
quick one-off workaround, and you'll probably eventually end up needing to use 
this method for one reason or another. One very common reason to use such a 
manual method of resolving names is in the case where you're testing a replacement 
server. In that case, you can configure the 
/etc/hosts
 file to have the same name as 
the original server, but with the IP address of the new server. Once you finish testing 
and confirm that the new server is operating properly, you can then replace the 
network-wide DNS name to point to the new IP address.
On legacy Ubuntu servers, the 
/etc/resolv.conf
 file included the IP addresses for 
DNS servers the system would use to resolve names. If you wanted to override the 
DNS servers for your server, you would alter that file. Although this file still exists 
in Ubuntu 20.04, it's not actually used anymore for this purpose. Name resolution 
is now handled by 
systemd-resolved
, which is a systemd unit that runs in the 
background and applies DNS settings based on what the system receives via DHCP 
or what you may have configured in Netplan. For the sake of completeness though, 
here is a brief overview of the syntax of this file in older releases, in case you end up 
working on such a server. An example of this file is as follows:
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by 
resolvconf(8) 
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN 
nameserver 10.10.96.1 
nameserver 10.10.96.2 

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