User updateable /etc/hosts

The DNS resolution provided on the local machine via /etc/hosts isn't updatable by a user account, which makes the following use-case a problem without root access :

DNS can be used as a poor-man's microservice resolution system, whereby a given microservice name can be switched to point from a local development machine to a remote testing machine, to a production machine purely (and immediately) by adjusting DNS entries.

Cleanest way didn't pan out...

One solution considered was to install a local DNS server. However, while the obvious choice (dnsmasq) can make use of one or more --addn-hosts files and even watch --hostsdir directories for updated files - the addresses there are cumulative - so that if an address is flipped from one IP to another and back, both IPs will be returned in a round-robin fashion. To reload the configuration requires a SIPHUP that a regular user cannot (?) issue. This eliminated this almost-clean route.

At the end of a lengthy internal debate, the cave-in approach was chosen : Change the mode of /etc/hosts to allow the dnsmasq group (or another suitable one on your machine) to have rw permissions, and grant your user access to that group...

Change permissions

Simply change permissions on the /etc/hosts file :

chmod g+w /etc/hosts
chown root:dnsmasq /etc/hosts
ls -l /etc/hosts

usermod -G dnsmasq myusername

Test the user's new permissions

The change will be system-wide upon next login. But can also be used immediately in a terminal in the current boot-cycle using :

su -i -u  $(whoami)

Done (with a bit of a sigh).