[Lxc-users] How long the dhcp lease lasts

[Michael H. Warfield]

On Mon, 2013-04-22 at 22:58 +0200, Robin Monjo wrote:
> Thank you for your answer.
> I want to have the hostname and ip written in the /etc/hosts file so I
> can access them directly using their hostname and not their ip. For
> example, I'd like to ping the hostname rather than the ip.

But...  You should get that from dnsmasq and not need them
in /etc/hosts.  That's the whole point of the DNS system.  Reliance
on /etc/hosts is old old stuff that was intended to be replaced by the
DNS system ages ago.  We should only need to rely on /etc/hosts for
local things and very rare exceptional conditions.

> I will document myself on dnsmasq to get a better understanding of everything.

Cool.  In most cases, dnsmasq can deal with DNS issues.  You have to be
sure that your host server references it, though, in /etc/resolv.conf
(i.e. "nameserver 127.0.0.1) or it won't now where to ask.  You then
configure other domains under /etc/dnsmasq.d/ since dnsmasq is a limited
forwarding / caching server.  To go "full bore" will a full dns server
and dhcp server, you would use the dhcpd package and bind (Berkeley
Internet Name Daemon) package but that's probably overkill in your case.

Regards,
Mike

> On Apr 22, 2013, at 10:48 PM, Michael H. Warfield <mhw at WittsEnd.com> wrote:
> 
> > On Mon, 2013-04-22 at 21:59 +0200, Robin Monjo wrote:
> >> Hello everyone,
> >> 
> >> Using the default config, containers will have their IP attributed by
> >> the dnsmasq service. I'd like to write in the '/etc/hosts' file of the
> >> host system the hostname and the corresponding IP address of each
> >> container I start.
> > 
> > Why?  If you're using dnsmasq, it's in the DNS cache of the dnsmasq
> > server.  That's its purpose in life, to act as a DNS caching service.
> > Why do you need it in /etc/hosts when you've already got in in DNS?
> > 
> >> I will then use this hostname in an iptable rules for port forwarding.
> >> But what if dnsmasq change an IP at the end of the lease ?
> > 
> >> So the question is: how long an IP given by dnsmasq will last ?
> > 
> > What is your lease expiration configured for?  I've used anything for a
> > few hours (high turnover large WiFi sites) to several days to carry over
> > a weekend along with static leases for servers and "permanent" devices.
> > It depends on what you've configured it for.
> > 
> >> May I see one of my container have its IP changed ?
> > 
> > Maybe.  Depends on what you've configured it for.  I'm not so sure about
> > dnsmasq acting as the dhcp server (which is what you are talking about)
> > but dhcpd will notify you of things like this.  Most notably, you will
> > get deletes on old name/addresses and adds for new name/addresses both
> > forward and reverse, but it's all configuration driven.
> > 
> >> Any ways to have the dnsmasq table synced with the /etc/hosts file
> >> (container's host side) ?
> > 
> > Again...  Why?  Use the DNS cache in dnsmasq.  You have no need to refer
> > to /etc/hosts at all.
> > 
> >> Kind regards
> > 
> > Regards,
> > Mike
> > -- 
> > Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
> >   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
> >   NIC whois: MHW9          | An optimist believes we live in the best of all
> > PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
> 
> 

-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
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