/etc/hosts handling plugin for unbound

[Paul Wouters]

On Mon, 19 Dec 2022, Petr Menšík via Unbound-users wrote:

> Is there some plugin for automatically watching /etc/hosts file for changes 
> and loading them as a local data?
>
> I am thinking about supporting unbound as a default localhost cache. But I 
> think many people rely on /etc/hosts changes are propagated automatically to 
> the cache. Dnsmasq and systemd-resolved both try to watch this file and 
> re-read it after changes.
>
> Is there any existing way to populate local data automatically from it? Is it 
> already possible to synchronize local data in unbound with legacy text file?

Any real software uses /etc/nsswitch.conf which states something like:

hosts:      files myhostname mdns4_minimal [NOTFOUND=return] dns

The "files" directory (see man nsswitch.conf) reads in /etc/hosts first.

This happens before the "dns" entry, so before unbound is used. So for
apps on localhost this should work fine? It is always read (and not
cached)

But I guess you want to make it systemd-resolved+glibc hack compatible,
where calls to gethostbyname() are intercepted outside of nsswitch by a
linux glibc hack, then fed to systemd-resolved, which I guess might do the
wrong thing by using dns before files ?

Or are you trying to work with the libunbound call of:

         /* lookup from /etc/hosts before DNS lookups as people expect that */
         ugh = ub_ctx_hosts(dns_ctx, "/etc/hosts");

and are afraid changes in /etc/hosts are not picked up without an
unbound restart?

I guess I feel /etc/hosts is there only for localhost apps in case of
broken DNS. The days you could leave something out of DNS by putting in
the /etc/hosts file are kinda long gone.

Perphaps you can detail a bit more of what you are looking for and what
you are afraid of ?

Paul