[ale] /etc/hosts and caching

[Jim Kinney]

Since nscd is a name service caching daemon it's what you do want to use.
There are some gotchas:
If the system is not running networking before nscd starts, it will never
get any data as it never loads the system nameservers.
Changing data in hosts will not get picked up by nscd until it's refresh
time has expired. That time is a conf file option.
Restarting nscd will not resolve either of these.
The solution is to do a cache flush on the hosts entries in nscd.
Man nscd for exact syntax.
Use nscd. It's a good tool for offloading network traffic that's basically
redundant data. If you set a ttl of an hour, that works well for normal use.
On Nov 4, 2011 8:26 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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