Re: [RFC PATCH 0/1] Create a DNS SRV record of the ID mapping domain

[Steve Dickson <SteveD@redhat.com>]

On 05/24/2016 02:20 PM, Chuck Lever wrote:
>>>  $ nfsidmap --txt
>>> >> 
>>> >> could retrieve it and display it,
>>> >> 
>>> >>  # nfsidmap --txt -s
>>> >> 
>>> >> could retrieve it and update idmapd.conf if
>>> >> there was a TXT record retrieved, for example.
>> > I see what you are trying to do here... instead 
>> > of rewriting idmapd.conf... we should probably
>> > uses... the system that shall go nameless... systemd! ;-)
>> > 
>> > systemd could run the nfsidmap --txt command that would
>> > create a file under /run, which is managed by the
>> > systemd-tmpfiles package. rpcbind does something similar
>> > to manage its warmstart up files. 
>> > 
>> > Then we could point rpc.idmap and nfsidmap to that
>> > runtime file via the libnfsidmap interfaces.
> Or provide a setting in /etc/idmapd.conf which is
> the pathname of the /run file.
> 
> It's a little nicer if these settings were all in
> one place instead of split between /etc/sysconfig,
> systemd configuration, and idmapd.conf.hostnamectl
I agree... but... we are dealing with systemd which 
limits your options when it comes to reading in
configuration files.

> 
> No Domain= setting means:
> 1. use the contents of the /run file
> 2. if no /run file exists, or it's empty, use the
> current mechanism to determine the ID mapping
> domain name
Right... but changing the name of the /run file
really does not have to changeable, IMHO... 
 
> 
> How does hostnamectl work? does it use /run files?
Taking a quick look it appears not to... I see a lot
of dbus code... It does not look too interesting to me. 

> 
> 
>> > The problem with this is how do we expire this cache?
>> > We would have to store the TTL to know when its time
>> > to ping DNS again... Is the TTL returned in the DNS
>> > query?
> I'm not aware of any required caching semantics
> (again, no real standard here).
> 
> I wouldn't expect this setting to change very
> often. Perhaps once per boot, or once per system
> wake-up, or whenever there is a network configuration
> change, is good enough. My guess is you don't want
> this changing arbitrarily with running users on
> the system. So maybe once per boot is the right
> answer.
Fine... we can deal with expiring the cache if
it becomes an issue... 

> 
> "nfsidmap --txt -s" could force a refresh by hand.
True.

> 
> (Also we need to figure out how to break a tie
> on multi-homed systems where more than one TXT
> record is found; maybe the only thing to do in
> that case is use Domain= , but you'd kind of
> prefer good behavior without needing a manual
> setting).
Does that even work? How can you have multiple domains
on the same host? 

I would say we document the fact the first TXT record
processed is the one we go with. All others are ignored.

steved.