[Beowulf] are compute nodes always kept in a private I/P and switch space?

Mark Hahn hahn at mcmaster.ca
Wed Jan 13 13:37:39 EST 2010

>> on the workstation of the user. Other reasons are braindead license servers
>> which are not NATable. Like the ones used by Catia or LS-DYNA. Management
>> could be much easier when the administrator is able to contact every device
>> directly from his workstation.

I don't agree with the latter, at all.  the marginal effort of admining 
through another box is trivial.

> Oh! I thought NAT worked transparently  and the application didnt even
> realize it was NAT-ed. I didn't know some servers could have a problem
> with this.

a client using NAT will not know any different, but the _talked_to_ service
might, since it'll see multiple connections from the same NAT server 
address(es), and won't be able to originate a socket to the client.
(unless the NATer has some protocol-specific awareness like NATed FTP.)

we have all our compute nodes on private addresses and also disable NAT.
this does make it somewhat trickier to get external-hosted evil-type licenses 
to work (flexlm with vendor daemons).  but I'd say this is a fairly useful
dividing issue: clusters that are all-public tend to be personal-ish and 
small.  clusters that are larger and support very wide groups tend to be 
more tightly controlled.  I think the way to think of it is that if you
have a personal or limited-purpose cluster, you _do_ in fact want it to 
depend on (and wait on) external resources (licenses, fileservers, GUI apps).
for a large, broad-purpose cluster with lots of disparate users, it's very
important to minimize those sources of complexity and inefficiency.
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