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List:       jboss-development
Subject:    [JBoss-dev] [ jboss-Bugs-569305 ] Server IP detection causes problems
From:       "SourceForge.net" <noreply () sourceforge ! net>
Date:       2003-05-31 7:19:11
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Bugs item #569305, was opened at 2002-06-15 07:35
Message generated for change (Comment added) made by alanshields
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=376685&aid=569305&group_id=22866

Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Samuel Terrell (j3110)
Assigned to: Nobody/Anonymous (nobody)
Summary: Server IP detection causes problems

Initial Comment:
By default, on some Linux distributions, for
performance and other reasons (some interfaces have
dynamic IP's but the hosts ip shouldn't change), the
host name of the local machine is configured to point
to 127.0.0.1.  When connecting through JNDI from a
remote machine, the IP set in jndi.properties is
overwritten with 127.0.0.1 on the client side. 
Obviously, this causes the client to fail connecting to
the server.  Other servers, Apache for example, warn
the user that this is probably undesired behavior and
allow a way to manually override the local IP with an
option in the configuration files.

----------------------------------------------------------------------

Comment By: alan shields (alanshields)
Date: 2003-05-31 07:19

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Ive had a couple of issues with this where the ip address of the name 
returned by hostname is not the address of the server.

With an AIX HA cluster this appears to be quite common, eg with a two node 
HACMP configuration:

servera - hostname of machine a
serverb - hostname of machine b
service - service name

machine a's host file
...
...
192.168.42.100 service
192.168.42.101 servera
...
...

machine b's host file
...
...
192.168.42.100 service
192.168.42.102 serverb
...
...

the 101 & 102 addresses exist at boot up, once one of the two machines 
takes control of the service address it's boot address is no longer available, 
now when jboss starts up (on machine a for instance) it looks up the 
hostname (servera) then looks up the ip address for that (192.168.42.101) 
then attempts to connect to itself on that address and fails.


----------------------------------------------------------------------

Comment By: Samuel Terrell (j3110)
Date: 2003-01-16 19:56

Message:
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Being a developer too, I've given this much thought.  I
assume the server sends the IP back because of the
possibility that the bean requested is on a different server
in a cluster or the JNDI server has a different IP than the
container.  

The root of this problem is that DNS records don't always
exist for a particular server.  Some people run load
balaners or multihomed networks or firewalled networks that
have a different IP than the local machine for the DNS
record.  In these situations, all the traffic that is to get
to the "Bob" domain will hit an IP on a router, firewall, or
load balancing system.  From there, it will forward it (or
not) to a particular client who has no dns record.  Usually,
it is a 192.168.* or 10.* address allocated for this
particular purpose.  This problem, as another poster
mentioned, is compounded when you have multiple internet
connections, multi-homed.  In this situation, you will
listen on a virtual IP address, but you want your clients to
connect to any address it can of a list that MUST be entered
by the admin.  There is really no way of detecting these
reliably, and it is a very common situation for anyone that
wants true HA and performance.  For example, most ISP's that
offer coorperate web hosting that is reliable will have a
connection through Sprint and one through Qwest or MCI or
anyone else.  That way when one of the backbones of the
internet gets DOS'd/struck by lightening, only the poor saps
that use their backbone will not have a connection to the
server.  

What we end up with, in order to make a server work in all
conditions, is slightly complicated.  Other servers get away
with this because they allow you to pass back host names
that use DNS to resolve to the multiple IP's they connect
to.  This may work with JBoss, but it will not know which IP
to listen on, and it can't listen on all interfaces.  If it
listens on all interfaces, then it will interfere with 
multipath routing daemons.  What we need is a place to
specify ListenIP, and a place to specify Hostname that may
be different from the system hostname.  Look at the JavaDoc
for ServerSocket's constructors.  They have a special
constructor for this situation.

The ideal solution is to be able to overide the defaults and
set a list of ip's to bind to and listen on, and to have a
seperate list that can be overridden to specify a list of
IP's that clients will connect to.  I say IP's for both
because if you use DNS, then 1 DNS name could refer to all
the servers in the cluster.  If your architecture forwards
requests from one server to another, then you will be ok
with this, but some people don't want/have a DNS name for
their servers as well.

I hope I was more informative and helpful this time around
(now that I've thought out the problem a little more).  Make
whatever decision you think is best, in the past you've all
done a great job of balancing the needs of your clients!

----------------------------------------------------------------------

Comment By: Jens Deponte (dirkgently)
Date: 2003-01-16 13:32

Message:
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Recently I came across the same bug and changes my
/etc/hosts file as a workaround. Although everything went
fine since, I'm not quite satisfied with this solution.
Setting the servers IP address via a config file seems to be
a good solution, but it fails for a multihomed host behind a
NAT firewall. This might be a uncommon configuration, but by
now I don't see a reason, why the server should deliver its
IP address anyway. If the client could connect with the
address configured on client side, why can't it continue to
do so?
Any suggestions? Otherwise I'll have to ask the source code :-(

Details: The server I used is a Linux (SuSE 8.1) box
configured using DHCP. The default configuration of this
distribution with DHCP is hostname => 127.0.0.2. You can
discuss if this is ok or not, but the bug should also be
reproducible with any JBoss installation behind a NAT firewall.

----------------------------------------------------------------------

Comment By: Samuel Terrell (j3110)
Date: 2002-06-19 07:59

Message:
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You would think that since you specify the IP in the
jndi.properties file that the client could connect to the
server, and it does for a brief moment.  In that moment,
apparently it retrieves the incorrect IP address from the
JNDI server.  The reason I say this is that I get a
connection refused error on the client.  It explicitly
states that the error occurred while trying to connect to
127.0.0.1, and the error is thrown in the JNDI lookup of
anything from a remote machine.  I thought this was funny
and set the server's host name to point to 1.1.1.1 in
/etc/hosts, and it returned that address.  As soon as I
noticed this behavior, I was able to set the server's host
name to point to the same IP as it is in the jndi.properties
file.  The client worked fine after I did so, but other
users of JBoss probably will never notice this behavior, and
thus, think that JBoss is to blame.  Technically, JBoss
should probably fail if it retrieves an IP in the
127.0.0.0/8 range, because it is certain to not work from
remote machines.  In the very least it should warn the
unsuspecting administrator that he/she needs to fix the name
resolution so that it doesn't end up with 127.0.0.1 for the
host name.  I'll leave the judgment of what the proper
behavior should be up to someone else.  I'm certain that
this behavior wasn't intended as it causes remote
connections to fail by default to a Linux server running JBoss.

Basically, it isn't necessary that the server sends the IP
address.  In fact, if it didn't, this problem wouldn't
occur.  I have confirmed this behavior on several machines.
 If you want to see the behavior yourself:
Set up JBoss on Linux.  Type “hostname”.  Edit /etc/hosts.
Make sure the only line with the return of the “hostname”
command is the same line as 127.0.0.1.  Run JBoss on the
server.  Edit jndi.properties on the client machine (must be
remote, not just different VM) .  Set the IP to the proper
IP of the server.  Then try to run your client application.
 If you properly configured Linux, you won't have to check
the “hostname” command against /etc/hosts, as it is the
proper behavior of Linux to tell applications to use the
local interface for local connections.  The problem arises
when servers like JBoss use this method of getting the IP to
tell the client.  You indeed will have the same problem from
apache if the host name of the local system doesn't lookup
via DNS, not the hosts file.  But, when you have this
problem from apache, it will say “Cannot find server name,
using 127.0.0.1” as well as giving you a method for
overriding this automatic detection mechanism in the
configuration file.

----------------------------------------------------------------------

Comment By: Joao Pedro Clemente (jpcl)
Date: 2002-06-18 19:35

Message:
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For what I've read from other J2EE platform manuals, I guess 
this happens 'cause of misuse of IP address. I'm not sure if I 
understood the failure cenario completely, but it seems that 
this would not happen if the client would use the server name 
instead of ip address. This is similar to some failures that 
happen when using a http proxy server that badly resolve dns 
names, if I'm not mistaken.
Is it really necessary that the server sends the IP address to 
the client? Are you sure this is not a problem of your 
machines network configuration? Maybe you could give more 
details on your setup/machine configuration?

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=376685&aid=569305&group_id=22866


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