[ale] /etc/hosts and caching

Fri Nov 4 08:58:18 EDT 2011

I would also like to see some facts, but google turns up tons of “issues” with it (nscd).  As a result we might be looking at installing Bind DNS caching only on the servers we are talking about.

Damon at damtek.com

From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of leam hall
Sent: Friday, November 04, 2011 8:31 AM
To: Atlanta Linux Enthusiasts
Subject: Re: [ale] /etc/hosts and caching

I use it as it is turned on everywhere I've worked. I've not seen any data that suggests it is a problem, but I'd be happy to see some facts.

Leam

On Fri, Nov 4, 2011 at 8:24 AM, Chesser.Damon <Damon.Chesser at suntrust.com> wrote:

Thanks for the reply, that is how I thought it worked also.  As for nscd, someone on this list said “Don’t.  Use. It.”  

Any other opinions on it?

Damon at damtek.com

From: ale-bounces at ale.org [mailto:ale-bounces at ale.org] On Behalf Of leam hall
Sent: Friday, November 04, 2011 8:17 AM
To: Atlanta Linux Enthusiasts
Subject: Re: [ale] /etc/hosts and caching

Good morning Damon!

As far as I can tell by editing /etc/hosts on a RHEL 4 box, the IP addresses are not cached longer than it takes me to edit the file. I believe your server will alwyas look in /etc/hosts anyway, per the /etc/nsswitch.conf file. The normal hosts line is something like: 

   hosts:      files dns

There is the program nscd and it's config file, ncsd.conf. This configures some caching for you but I *think* it's more DNS related than affecting /etc/hosts. 

Hope that helps.

Leam

On Fri, Nov 4, 2011 at 7:40 AM, Chesser.Damon <Damon.Chesser at suntrust.com> wrote:

This dovetails into building a DNS caching server I asked earlier this week.  The issue is we are seeing latency in our application and a possible (but only possible, not proven) issue might be host lookups.  I figured that an entry into /etc/hosts would be faster than a WAN DNS lookup especially since the IP is static.  Someone was concerned with disk reads and that becoming a bottleneck.  Someone else pointed out that /etc/hosts file was cached.  

This started a google search by me to find out if that was true or not.  Totally inconclusive.  Some have reported issues with not being able to get the Linux box to re-read the hosts file after a change was committed short of a reboot or init restart.  Others have said just make the change and it shows up.  I have not found any documentation saying whether it was cached or not.  Any smart guys know the answer or can provide any documentation on that?  It’s kind of funny, you think you KNOW something until someone says “Prove it”.

Damon at damtek.com

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