Subject: Understanding localhost
From: "John A. Sullivan III" <jsullivan@opensourcedevel.com>
Date: Fri, 01 May 2009 04:48:12 -0400

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.  That's fine and we can accommodate it by leaving our
settings as they were but I wanted to make sure I hadn't missed
something.  Thanks - John
-- 
John A. Sullivan III
Open Source Development Corporation
+1 207-985-7880
jsullivan@opensourcedevel.com

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