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 . host host1.example.com 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 , /etc/auto.master : /misc /etc/auto.misc /etc/auto.misc : test host1.example.com:/tmp 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. http://ftp.kernel.org/pub/linux/daemons/autofs/v5/autofs-5.0.3-remove-redundant-dns-name-lookups.patch
(In reply to comment #0) > The problem is also seen with autofs on RHEL 5. That's true. > > Using the following patch fixes the problem. > http://ftp.kernel.org/pub/linux/daemons/autofs/v5/autofs-5.0.3-remove-redundant-dns-name-lookups.patch 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.
The test packages resolve the issue on RHEL 4. The DNS lookups no longer increase with higher number of ip addresses associated with the hostname. If the hostname is associated with 1 ip : 2 DNS lookup 3 ip : 2 DNS lookup 4 ip : 2 DNS lookup 5 ip : 2 DNS lookup
Committed in autofs5-5.0.1-0.rc2.108
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: Previously, the number of DNS lookups corresponded to the number of IP addresses returned from a host name lookup for a single NFS server. NFS servers which resolved to multiple IP addresses increased the number of DNS lookups and caused excessive system load. This update removes redundant DNS lookups for NFS servers.
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. http://rhn.redhat.com/errata/RHBA-2011-0241.html