Red Hat Bugzilla – Bug 495895
autofs5: large number of DNS lookups for hostnames associated with multiple ip addresses.
Last modified: 2010-10-23 05:01:04 EDT
+++ This bug was initially created as a clone of Bug #495890 +++
autofs5 produce massive number of DNS queries when one nfs server name is associated with many IP adresses. For example when one host has 40 IP adresses associated mounting one autofs directory produce ~160 DNS queries.
steps to reproduce :
1) Configure roundrobin DNS so that the autofs client resolve host1.example.com as below .
host1.example.com has address 10.65.6.193
host1.example.com has address 10.65.7.143
host1.example.com has address 10.65.7.225
host1.example.com has address 10.65.6.128
2) nfs server exports /tmp *(ro)
on autofs5 client , configure the map such as ,
Capture the network packets using tcpdump.
On the client cd into /misc/test.
Check the number of DNS queries in the captured dump.
The table below lists the number of host lookups for varying number of ip addresses.
1 ip : 2 DNS lookup .
2 ip : 14 DNS lookups
3 ip : 20 DNS lookups
4 ip : 26 DNS lookups
The problem is also seen with autofs on RHEL 5.
Using the following patch fixes the problem.
--- Additional comment from email@example.com on 2009-04-15 09:48:02 EDT ---
(In reply to comment #0)
> The problem is also seen with autofs on RHEL 5.
> Using the following patch fixes the problem.
Right, this is one of the few (I think there are probably only two
things actually) that haven't been back ported to 5.0.1 in RHEL.
Sorry about this, I'll get onto it.
This issue has been fixed in the latest autofs package
The autofs RHTS test bugzillas/bz495895 can be used to
verify this correction.
I'm afraid I must frop the manual umount recovery patch.
Internal regression testing has shown that it causes problems
with the autofs submount handling and after trying to fix it
for some time without success I have to concede defeat on
this, at least for now, as time has run out for RHEL-5.4.
At least this doesn't affect the fix for the root cause we
identified so, if you would like this further investigated,
please log a new bug and I'll revisit it for RHEL-5.5.
Sorry, for the inconvenience.
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Previously, when autofs looked up a host name where when one NFS server name was associated with multiple IP adresses, autofs would repeat the query many times. As a consequence of these multiple queries, the mount would take a long time. Now, redundant queries have been removed, so that autofs performs the mount more quickly.
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.