[K12OSN] Re: Tossing around an idea...need some input

David Trask dtrask at vcsvikings.org
Sat Aug 13 07:11:19 UTC 2005


So cool!  Getting to the idea of the script testing to see who's alive and
all (I like the DNS round robin idea a lot, but the idea of hostname after
the fact scares me as I know some apps do that...I've had issues...so
until I can explore further)....how would you write a script that would
ping a server....if alive...then so be it....but if dead....do the
following  "xxxx"   I have no idea how I would go about doing the whole
ping, response, if....thingy.  Any pointers?



"Support list for opensource software in schools." <k12osn at redhat.com> on
Saturday, August 13, 2005 at 2:53 AM +0000 wrote:
>> Now....notice the "next server" line up above and the    
>> 
>> option root-path              "10.0.15.253:/opt/ltsp/i386";
>> 
>> These are in the global section....one question I had is....if I put
>these
>> in the workstation declarations down below pointing to Server #2
>> (10.0.14.253 ) would that override the globals?  Example:
>
>Yes.
>
>Also, I wonder if you could set up internal DNS and use hostnames
>instead of IP addresses for the root-path and next-server.  Assuming
>for our discussion that your two LTSP servers are 10.0.14.253 and
>10.0.14.252, you would put this in your DNS zone file (after the SOA
>and all that):
>
>ltsp    A       10.0.14.252
>ltsp    A       10.0.14.253
>
>According to "DNS & Bind" (a book every administrator should have)
>this will give you Round Robin Load Distribution (p. 273).
>
>Your DHCP options would then be:
>option root-path        "ltsp.daves.school:/opt/ltsp/i386";
>option next-server      "ltsp.daves.school";
>
>The DNS server will alternate between the IP addresses.  Since the
>kernels on the two LTSP servers will be identical it probably doesn't
>matter that a given client could get the kernel from one server and
>root from the other.  And since (I assume) the client only mounts root
>once, each client should get its IP address for 'ltsp.daves.school',
>mount root, and be done with it.
>
>A problem could arise if a given client would need to ask for the
>LTSP server's hostname later on.  For example, if the client has an
>application running and that application creates temporary files on
>the server, and the client asks for "ltsp.daves.school" and gets the
>other LTSP server's IP address, then the client may try to communicate
>with the wrong server about the application running on the other
>server, and it might matter.  Or something like that.
>
>This is all assuming that those DHCP options can use hostnames instead
>of IP addresses, and I don't know for sure about that.  I guess
>I could test...
>
>/me tests
>
>It appears to work fine to use hostnames for those options in
>dhcpd.conf.
>
>
>> OR....another intriguing idea for failover is to have a script that
>pings
>> the servers (Server 1 and Server 2) to see if they are "alive"....it
>would
>> assume a dhcpd.conf pointing to Server 1.....but if Server 1 turns out
>to
>> be "dead"....do something like this....
>> 
>> Ping Server 1....if alive continue using dhcpd.conf.....if dead then...
>> 
>> service dhcpd stop
>> mv dhcpd.conf  dhcpd-serverone.conf
>> mv dhcpd-servertwo.conf  dhcpd.conf
>> service dhcpd start
>
>Yep, this is also a good idea.
>My preference would be to use a symlink for dhcpd.conf, pointing to
>one of your two confs.  Then, in case of trouble:
>
>$ service dhcpd stop
>$ ln -sf dhcpd-servertwo.conf dhcpd.conf
>$ service dhcpd start
>
>> this is crude I know, but just trying to illustrate the idea....
>
>Dude, that's how *nix works.  It is full of delightfully fun, crude
>stuff just like that.  :)
>
>/me has been reading the Unix Hater's Handbook.  It's not as good as
>BIND & DNS, but it's still worth reading.
>
>What I'm working on right now is a simple hot-spare setup...for
>any Linux box, but with LTSP in mind.  This would enable a low-end box
>with enough disk space to be a backup and pinch-hitting hot spare for
>a beefy LTSP server.  The spare may not be able to run [m]any thin
>clients, but it can certainly still do DHCP & DNS for a network with
>lots of non-LTSP boxes depending on it.  (Yes, this will consist
>almost entirely of 'rsync', but I want to have a text file listing
>config files *not* to overwrite on the spare *until you need to use
>it*.  And then I want a single command to move all the configs
>appropriately and give the pinch-hitter the bat.)
>
>Anywho, that's related to what you're working on so I thought I'd
>mention it.  :)
>
>--matt
>
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David N. Trask
Technology Teacher/Coordinator
Vassalboro Community School
dtrask at vcsvikings.org
(207)923-3100




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