On Wed, Dec 05, 2012 at 03:19:51PM +0100, Natxo Asenjo wrote:
> On Wed, Dec 5, 2012 at 3:11 PM, Jakub Hrozek <jhro...@redhat.com> wrote:
> > On Wed, Dec 05, 2012 at 02:20:40PM +0100, Natxo Asenjo wrote:
> >> hi,
> >>
> >> why would I want sssd to cache group/hostgroup/netgroup membership?
> >>
> >> Is the performance hit so huge on the ldap servers?
> >>
> >> I ask this because Windows admins are used to apply membership of
> >> groups to objects and the changes in a single site domain (or even in
> >> a multisite domain with fast wan links) are replicated very fast, it
> >> is nearly instantanous. So for those admins, having to wait x minutes
> >> for the sssd cache to expire is, to put it mildly, strange.
> >>
> >> What are the consequences of disabling the cache with an entry like this:
> >>
> >> entry_cache_timeout = 0
> >>
> >> in sssd.conf?
> >>
> >> Thanks in advance for your input.
> >
> > Feel free to tune down the cache timeout, it should just work. Speed
> > benefits depend on your configuration, I guess. With large group
> > memberships, the speed benefit of caching is quite visible.
> >
> > However, is it really that necessary to see the group memberships
> > updated with "id" for instance? One reason is that during login, the SSS
> > never just consults the cache, but always performs e.g. fetches the
> > group list for the initgroups operation for the server to make sure that
> > access control mechanisms have the latest group memberships available.
> is this the case too for hostgroups? I am bootstrapping an
> infrastructure with ipa and cfengine and I am seeing that it caches
> the hostgroups/netgroups information, so when I join a host to the ipa
> realm, I need to empty the netgroup cache or it will take 90 minutes
> to apply configs from cfengine based on netgroup info.

No, I'm afraid you'd hit the cache here. But in this case, as hostgroups
are translated to netgroups and looked up as netgroups, you can use a
separate timeout for netgroups only. See the parameter
entry_cache_netgroup_timeout in man sssd.conf.

> > So while lookups that only go through the Name Service Switch, such as
> > getent or id might display outdated information for some limited period
> > of time, authentication should never allow or deny access based on
> > obsolete cached data.
> well, this is apparently the case for me. I use the netgroup database
> from nss, so it is caching.


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