Thursday, July 23, 2009

OT: Mac OS X dns caching problem with VMWare

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I was working with one of my Vmware Fusion VMs, when the VM autoprotect backup started.
I don't like particularly the way this feature has been implemented in VMWare Fusion as it doesn't offer any scheduling option, it just based on some funny "elapsed time since last backup" setting that changes depending on when you turned off and on the VM in the meanwhile, which is really a crazy thing in my humble opinion.
Back to my problem, once the backup was finished, just a couple of minutes later, as soon as i tried to navigate the apex application i was working on, i got weird HTTP 404 errors. This was happening both with Firefox and Safari, which made me think that the problem was not at the browser level, but somewhere else.
Restarting the VM had no effect whatsoever.
Fortunately, before attempting some fancy and desperate options, i tried connecting using the straight IP address of the VM instead of the DNS i am using all the time and it worked.
This convinced me that something wrong had happened with the DNS server or DNS cache, however, oddly enough, executing ping servername.local from Mac's terminal application was working just fine.
Is ping skipping the DNS cache perhaps?
Don't ask me.

After a quick search I could find on the web the command to flush the DNS cache on Mac OS X 10.5:

sudo dscacheutil -flushcache

Thereafter, with some satisfaction, the browsers resumed working properly using local dns names.

Why did the VM autoprotect backup mess up the DNS cache in the first place?
I am quite sure this was not the first time the autoprotect ran, why did i need to flush the dns cache this time?

Useful answers are welcome, indeed i got some preliminary feedback from the VMWare forum.

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