[SSSD] [PATCH 1/2] Set default DNS resolution timeout to 15 seconds.

Simo Sorce simo at redhat.com
Thu Jul 4 17:45:02 UTC 2013


On Thu, 2013-07-04 at 16:23 +0200, Michal Židek wrote:
> https://fedorahosted.org/sssd/ticket/1966 (SSSD failover doesn't work if 
> the first DNS server in resolv.conf is unavailable).
> 
> The problem here is, that if first nameserver in resolv.conf is down, 
> the resolution is too slow and SSSD will not wait for the result of 
> ares_search and go offline. In my case the resolution was sometimes more 
> than a minute, because all search domains in resolv.conf were searched 
> inside ares_search() call using the first (not working) nameserver in 
> the first place and then with the working nameserver (and before that, 
> SSSD tried to figure out the domain name from my incorrectly set 
> hostname, which added more unnecessary DNS lookups).
> 
> To avoid this problem, the option dns_discovery_domain must be set 
> properly, so that only the correct domain is searched, but even that is 
> not enough, because the default timeout for dns resolver operation in 
> sssd is too low. This patch rises the default value to 15 seconds 
> (instead of 5 seconds).
> 
> Another option might be to lower the amount of time ares waits for a 
> nameserver to respond (currently it is 5 seconds, that is why 5 second 
> for the entire dns resolution is not sufficient), but I do not want to 
> do this.

Why not ?

5 seconds these days is quite awfully high all in all.
I think 1 second should be plenty in most cases, so maybe a default of 2
seconds should be considered.

> These patches also change man pages, so probably master only (string 
> freeze)? Even if this is a really small change.
> 
> I was also thinking, would it make sense to write a warning to the logs 
> if the dns_discovery_domain option is not set? It seem to be important 
> to set it properly for cases like this one.

I wonder, should we use the machine name to automatically set the
discovery domain, and only if that fails fall back to the ones defined
in resolv.conf ?

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York




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