[SSSD] How to tune the failover mecanism ?

Simo Sorce simo at redhat.com
Mon Dec 3 22:17:39 UTC 2012


On Mon, 2012-12-03 at 16:54 -0500, Dmitri Pal wrote:
> On 12/03/2012 04:27 PM, Simo Sorce wrote:
> > On Mon, 2012-12-03 at 16:16 -0500, Dmitri Pal wrote:
> >> On 12/03/2012 03:21 PM, Simo Sorce wrote:
> >>> On Mon, 2012-12-03 at 21:12 +0100, Olivier wrote:
> >>>> I may be wrong but that is not exactly the way I read the man page :
> >>>> http://linux.die.net/man/5/sssd-ldap
> >>>>
> >>>> On failover section :
> >>>>
> >>>> --> Further connection attempts are made to machines or services
> >>>> marked as offline after a --> specified period of time; this is
> >>>> currently hard coded to 30 seconds.
> >>>>
> >>>> As I understand it, once a machine or service has been stamped "offline",
> >>>> then it won't be queried before 30 second has passed.
> >>>>
> >>>> The delay I would like to know (and to tune if possible) is the time after which
> >>>> sssd query the next ldap server in ldap_uri list if the current one is
> >>>> not reachable
> >>>> (IMHO, 5 second would be more than enough and I think would even tune less
> >>>>  if I could).
> >>> Ah I think you've been mislead by the timeout section.
> >>>
> >>> That doesn't apply to a specific server but to a general attempt to go
> >>> online.
> >>>
> >>> If I remember correctly, when SSSD tries to go online it will try the
> >>> first server, and if it fails it will immediately try the next and so on
> >>> until it finds one that works or goes back offline because none work.
> >>>
> >>> If it goes back offline it will wait at least 30 sec. before going
> >>> online but will go online only if there is an event that requires data
> >>> after the 30 sec. has gone by.
> >>>
> >>> HTH,
> >>> Simo.
> >>>
> >> I think the question is for how long SSSD waits to detect that the
> >> server is offline and whether this is configurable.
> > It is not, SSSD will find out the first time it needs to resolve
> > something and will try to fetch data from the offline server.
> >
> > At that point it will determine the server is offline.
> >
> > What we may do is to retry immediately once, I do not recall if we do
> > that.
> >
> > Simo.
> >
> Let me try again...
> 
> SSSD sends a request to the central server because something triggered a
> lookup.
> How long SSSD waits to declare that server is not reachable before
> trying another server?
> What is the length of this timeout and is it configurable and how?
> 
> Does the question makes sense now?

It depends on a number of factors, as communication to the server
depends on various components like dns resolution.

For dns resolution we have a config option called dns_resolver_timeout
(default 5 sec), then for ldap we have other knobs like
ldap_search_timeout, ldap_enumeration_search_timeout,
ldap_network_timeout, ldap_opt_timeout, as well as
ldap_connection_expire_timeout

See the sssd-ldap manpage for details about these timeouts.

Simo.


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




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