[Mulgara-general] RMI server not running?

Paul Gearon gearon at ieee.org
Tue Jun 12 15:59:07 UTC 2007


On 6/12/07, Gok Mop <gokmop at gmail.com> wrote:
>
> Netstat has only one entry, but it's there.
> tcp6       0      0 localhost:39872         localhost:rmiregistry
> TIME_WAIT
>

I've never pointed nmap at rmiregistry before, but I just thought I'd try it
now.  It turns out that on most scans port 1099 does NOT show up, even when
everything is working just fine.  So maybe this isn't the problem for you
after all.

That being the case, maybe it *is* a server name issue....

<snip/>

> Speculation...
>
> So if there's nothing obvious wrong with mulgara, it must be something on
> my network.  The complication that I'm going to have to go research is the
> way mulgara resolves the host.  I am behind a cable modem, (and home router)
> with dyndns as a hostname.  I configure mulgara and tell it to use my local
> network name, but it consistently wants to resolve my hostname back to my
> cable provider's temporary host name.  (The home router is configured to
> forward all traffic to this machine on ports 8080 and 1099)
>
> Because the linux machine probably isn't smart enough to know itself by
> the cable provider's dynamic hostname, the way mulgara resolves the hostname
> may cause it to route traffic back to my router.  The question is, is my
> router smart enough to route *internal* network traffic back to an
> *internal* host, or are its port forwarding rules strictly applied to
> traffic originating from *outside* the network?
>

Most routers don't like this this.  Even when you can (I've set this up
before) it's not something that can be set up by default, since the router
has to be told that the public address is to be forwarded to the internal
address (you're using port forwarding, right?)

In any case, it probably isn't mulgara.  Still, assuming this speculation is
> related to my problem, it would be nice if mulgara didn't try to change the
> hostname on me...if it would just use the hostname or IP address I give it
> through configuration or URIs.
>

How do you think it is changing the hostname?

The code in question takes the machine name in the URI (localhost in your
case) and connects to that.  It then sends the entire URI along when talking
to models on that machine.  When a server gets a graph URI, it converts it
to a canonical form before storing it (in the system model) but that's the
only change.  So if your computer is called "myhost.mydomain" and is on
192.169.0.1, then the following queries will all be identical:

select $s $p $o from <rmi://localhost/server1#mydata> where $s $p $o;
select $s $p $o from <rmi://127.0.0.1/server1#mydata> where $s $p $o;
select $s $p $o from <rmi://myhost.mydomain/server1#mydata> where $s $p $o;
select $s $p $o from <rmi://192.168.0.1/server1#mydata> where $s $p $o;


NB: There *is* an issue with the canonical form of the graph that is used
internally, but that won't be affecting you.  (it's a problem if an existing
database is brought up on a host with a different name - like a notebook
that moves between networks).  It was fixed in Kowari, but Brian is in the
process of re-doing it for Mulgara.  He should have it done Real Soon Now
(TM).


So maybe you'll have some more luck if you try some different names.  Let me
know how it goes.  As I said, I have some minimal RMI code based on what
Mulgara does (<50 lines), so we can narrow down your problem if needed.

Paul
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