[RFC] DNS system upgrades

A few things are on my radar that need improving in the Squid DNS
components. I am proposing these as a batch, any which we can agree on
will be scheduled for fixing in 3.4.

1) renaming all DNS options to begin with dns_* prefix.

This will allow the cfgman documentation to collate these options
together as a batch in future.
Also clarify what component in Squid some of the more obscure options
relate to.
Also, allow for some future upgrades compacting these type of options
into a single component directive / command line interpreter simplicity.

Options affected that I'm aware of:
   append_domain
   ignore_unknown_nameservers
   hosts_file
   cache_dns_program ... (stripping the cache_ part.)

NP: at this point I am on the fence about adding the prefix to fqdncache
and ipcache options and *not* proposing a change to them.

2) adapting append_domains from a string type to a custom type

This will allow us to do additional configuration validation. Such as
identifying whether resolv.conf or squid.conf was used as data source.

* auto-enablling dns_defnames search list

/etc/resolv.conf contains two similar but different directives for
labelling the local domain name.

The "search" directive in particular signals DNS searching of multiple
domains to the default host resolver. But Squid still requires explicit
"dns_defnames on" in squid.conf to enable that behaviour. As a result we
have administrators seeing a 'bad' difference between internal and
dnsserver when they try upgrading to internal DNS.

I propose using the resolv.conf hint to enable dns_defnames searching
automatically in the absence of explicit squid.conf configuration.

Administrators who do not want it are supposed to be using the
alternative "domain" directive, when they use tools like host or
nslookup to debug they should see consistent behaviour (diverting them
away from Squid to the actual DNS issues in resolv.conf settings), and
this will prevent future confusion such as appears to be happening in
bug 3585.

3) removal of dnsserver and related code.

IRIC the argument for keeping it previously was NetBIOS or WINS name
lookup still being needed (though I am suspicious the dns_defnames issue
was the actual cause of this).

  - NetBIOS was deprecated in 2000, to be replaced by DNS
  - WINS was deprecated in 2012, to be replaced by IPv6
auto-configuration / adhoc services.

I am okay to see this delayed a few more squid series to give WINS
longer to die, but it is time we looked again at why it is still there.

Since the last round of discussion we adjusted the internal engine to
fix most of the remaining issues. The above dns_defnames behaviour
change is the last bit I am aware of that is needed for a seamless
upgrade, short of full-blown NetBIOS support integration which is not
very feasible.

Amos
Received on Wed Feb 20 2013 - 00:08:33 MST