[CentOS] NFS / DNS problem

Wed Aug 15 11:39:36 UTC 2007
Andreas Rogge <arogge at gmx.de>

Hi Simone,

what nameservers are configured for the nfs-servers?

Afaict the nfs-server does forward and reverse lookup the clients. So if 
your nfs-server's DNS breaks (i.e. if only ns0 is configured there and 
you shut down ns0) you might see the issue you described.

Regards,
Andreas

Simone schrieb:
> Hi all,
> 
> Today we have had a strange problem that has taken down our website, we 
> understand what happened but not why so I am hoping someone has seen 
> this before.
> 
> We have our web servers (web1 web2 web3 ..... web10) mounting an NFS 
> share (/export/data) from server nfs1. On the web server side we use 
> autofs in the format nfs-dedicated:/export/data where nfs-dedicated is 
> an alias in our internal DNS servers pointing to server nfs1. We run a 
> primary and a secondary DNS (bind) server ns0, ns1 authoritative for our 
> zones and our webservers have them configured in /etc/resolv.conf
> Today we had to run some upgrade on the dns servers (bios firmwares etc) 
> so we took down ns0 and with it our website went down.
> All the nfs shares disappeared from the web servers (the logs show 
> requests to mount/unmount timing out), but at the same time on nfs1 the 
> logs show requests (mount and unmount) coming from the web servers and 
> no errors.
> 
> As soon as ns0 is back up, all gets back to normal. Minutes later we 
> take down ns1 for maintenance and it doesn't have any impact on the 
> website.
> 
> dig @ns0 nfs-web gives exactly the same results on ns0/1
> 
> Back to the office we try to reproduce the same scenario configuring 
> iptables on web3 to block traffic to ns0 but the server (web3) keeps 
> working fine reverting to ns1 for name resolution (as you would expect).
> 
> Has anybody seen this happening before? Any comment/suggestion much 
> appreciated.
> 
> Thanks
> 
> Simone
> 
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