I am in the process of upgrading my production server from Ubuntu 14.04 to 18.04 and noticed that there is something called
systemd-resolved in 18.04 which run a local DNS cache of sorts. 
Why is this required? What is wrong with simply putting
nameserver 184.108.40.206 or
nameserver 220.127.116.11 in
/etc/resolv.conf and calling it a day? Is it safe to disable
systemd-resolved and revert to the simpler configuration?
 I noticed only because it is randomly crashing and causing all hostname lookups to fail, effectively crippling my app - https://askubuntu.com/questions/1117842/systemd-resolved-crashing-with-failed-to-set-up-mount-namespacing-invalid-argu