[lvs-users] Load Balancer Not Listening on Specified Ports

mojorising moj0rising at aim.com
Mon Nov 2 21:19:52 GMT 2009

Okay. I've finally had time to come back to this. I've looked over
your latest message and now think I'm kinda stuck.

I checked /var/log/messages and see those same nanny messages like this:

Nov  2 11:59:20 omsbuild nanny[25772]: READ to timed out

but I don't see anything more from nanny on my system. Is there
another place on the server I can get nanny log information?

The ipvsadm commands are helpful to know, yet there isn't much for
them to report right now:

[root at omsbuild ~]# ipvsadm -L
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  ganassi.radius.co:webcache lc

[root at omsbuild ~]# ipvsadm -L --stats
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port               Conns   InPkts  OutPkts  InBytes OutBytes
  -> RemoteAddress:Port
TCP  ganassi.radius.co:webcache          0        0        0        0        0

Can you think of anything else I can do to find more clues on what
might be the matter?

Thank you!


On 26/10/2009, Graeme Fowler <graeme at graemef.net> wrote:
> On Mon, 2009-10-26 at 11:18 -0700, mojorising wrote:
>> Thanks a lot for your response. It helps me understand a bit more
>> about how LVS works.
> Grand :)
>> So, as I mentioned in my first post, "The web servers are up and
>> running. I can download web pages successfully from them from my
>> desktop as well as directly from the
>> load balancer with netcat or similar." I just checked again and I can
>> download web pages from the real servers on port 80 with netcat or
>> telnet from the LVS machine. So we're all good there. Now I'm
>> wondering why nanny might have issues talking to the real servers on
>> 80.
> Only you can tell that one I'm afraid. Have you checked the logs which
> nanny produces?
>> As for the bits about the configuration, yes. You are right. I just
>> verified the IP addresses in the configuration and the ones I am
>> testing with via netcat and telnet are the same.
> Good.
>> With respect to the former, if nothing is listening on the load
>> balancer, maybe I am trying to use it the wrong way. On other load
>> balancers I have used, such as pen or BigIP, the load balancer is
>> actually listening and waiting for TCP connections, which it then
>> forwards on to the "balanced" nodes (real servers) on specified ports.
>> Basically, as far as PCs browsing the balanced sites know, that load
>> balancer *is* the web server. Does that make sense? So when I go to
>> test those load balancers to see if they work, I check to make sure
>> they are listening on the approriate port and try to connect to them
>> in the same way I would connect to a real server directly. Am I
>> supposed to be doing things differently with LVS?
> The two devices/systems you mention can work in mixed modes;
> "directing" (load balancing at L4) or "proxy" (load balancing at L7). L7
> apps must first terminate the TCP session themselves before sending
> making a further L7 connection on to the server.
> LVS works at L4 - TCP or UDP. It is not application aware, and it only
> ever routes packets based on some rule it's configured with. That's it,
> in a nutshell.
> To the client, as you state, the load balancer *is* the webserver as
> they connect to an IP address (the VIP) and replies come back from that.
> At the TCP or UDP level, the client application is unaware of the magic
> going on at the other end of the connection.
> To check how LVS is configured, you can either rely on nanny to tell you
> (how? I don't know) or use the ipvsadm command line tool:
> ipvsadm -L            # displays LVS table
> ipvsadm -L --stats    # displays usage stats
> ipvsadm -L --rate     # displays rate statistics
> [the -n switch can be used for numerical output]
> It's worth remembering at this point that nanny is an abstraction layer
> away from what's really going on behind the scenes; it monitors the
> servers and puts them into/takes them out of the server "pool" as
> necessary. It doesn't really do *any* load balancing itself.
> Graeme
> _______________________________________________
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