Re: [vserver] Understanding localhost

From: John A. Sullivan III <jsullivan_at_opensourcedevel.com>
Date: Fri 01 May 2009 - 23:34:47 BST
Message-Id: <1241217287.6353.57.camel@jaspav.missionsit.net.missionsit.net>

On Fri, 2009-05-01 at 18:05 -0400, John A. Sullivan III wrote:
> On Fri, 2009-05-01 at 23:34 +0200, Herbert Poetzl wrote:
> > On Fri, May 01, 2009 at 04:48:12AM -0400, John A. Sullivan III wrote:
> > > Hello, all. I'd like to confirm that I understand the way vserver 2.3
> > > is handling localhost and the loopback address.
> >
> > > Am I correct to understand that, unlike earlier version, the default
> > > kernel compilation makes it safe to use 127.0.0.1 on a guest? That is,
> > > each one is uniquely mapped and does not interfere with the host
> > > listening in 127.0.0.1? We can thus set our /etc/hosts files to use:
> > > 127.0.0.1 localhost localhost.localdomain etc . . .?
> >
> > > However, is it also true that daemon bindings to localhost will still be
> > > made to the address in /etc/vservers/<guest>/interfaces/0 and will not
> > > include 127.0.0.1 unless explicitly bound?
> >
> > > I ask because we were delighted to realize we could simplify our zimbra
> > > installation by leaving /etc/hosts at 127.0.0.1 for localhost. We then
> > > started retrofitting our other servers to do the same. Some of our
> > > servers communicate with sshd on 127.0.0.1. We had changed the
> > > configuration files to bind them to the non-loopback address, e.g.,
> > > 192.168.1.10 because of our old understanding of 127.0.0.1. We also
> > > changed sshd_config by removing the ListenAddress 192.168.1.10 so that
> > > it goes back to the default of binding to all interfaces.
> >
> > > This broke those applications. When we do a netstat -tln on the vserver
> > > guests, it shows sshd listening only on 192.168.1.10 (as an example) and
> > > not 0.0.0.0.
> >
> > if you disable the single IP special casing, this
> > will change to the expected behaviour ...
> Sorry to be showing my ignorance again but what is "single IP special
> casing" that I should be disabling? Thanks - John
<snip>
Ah, found it in the kernel configuration. Argh! I suppose that means a
kernel replacement and reboot.

So are Automatic Single IP Special Casing and Automatic Loopback
Assignment somewhat incompatible? Special Casing mentions improved
performance. What kind of penalty does one take by disabling it? Thanks
- John

-- 
John A. Sullivan III
Open Source Development Corporation
+1 207-985-7880
jsullivan@opensourcedevel.com
http://www.spiritualoutreach.com
Making Christianity intelligible to secular society
Received on Fri May 1 23:34:31 2009
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