On 03/08/2012 04:54 PM, Dmitri Pal wrote:
On 03/06/2012 01:30 PM, Ondrej Hamada wrote:
On 03/06/2012 05:47 PM, Dmitri Pal wrote:
On 03/06/2012 10:59 AM, Simo Sorce wrote:
On Tue, 2012-03-06 at 10:56 -0500, Dmitri Pal wrote:
[...]
For a read-only KDC we need to investigate what's the better
solution.
There are many ways we can handle the issue, one of the simplest is
probably to allow the RO KDC to use a special LDAP Extended
operation
against a full R/W server to get the user keys to sign,
authenticating
with a special R/O KDC principal. We can also investigate how MS
does
internal forwarding and do something similar as I suspect that's
something samba4-RODC will want to implement too, so we could share
some
of the development burden there.
Simo.
I do not think it is a good idea for the remote RO KDC to go back to
the main datacenter on every authentication without some sort of
caching. This is why I think that some kind of SSSD integration might
be due. If RO KDC would just pass the authentication to SSSD in some
way and SSSD would do the caching in case the office gets offline. I
understand that authhub as is will not work as the client sends time
stamp encrypted with password and SSSD needs plain text password as
credential. I do not know if there is a way to solve this without
actually sending the password in the tunnel. IMO it is more important
to make sure that remote office can have uninterrupted operation than
to worry about the password being sent inside the encrypted tunnel. It
is something that deployment should decide and weight risks against
convenience.
This is why MS does partial replication, ie allows the RODC to have
data
about the office users. It's complex and there are many ways to handle
it. We need to look at various options and see how they would work
against uses cases we want to support.
Simo.
Then may be Ondrej should start with formulating use cases and
requirements based on this discussion.
I see three possible use cases here, but only two should be considered
when speaking about consumer node:
1) The office that should rely on that replica is quite a big one
(hundreds of employees) or many different users are authenticating
against its replica or there are located admins, who need to do a lot
of write-operations. --> In this case I suppose the best solution is
to deploy master replica there.
2) Office that doesn't fulfil the conditions in 1) - not a desperate
need for write-operations on ipa-server, but the priority is to allow
(some) clients to authenticate and use available services even when
the network is down. --> We need a consumer with credentials caching,
authentication requests for non-cached users or write operations must
be forwarded to master.
3) Office that doesn't fulfil the conditions in 1), but the priority
is security, so that the consumer is not allowed to store or cache any
confidential data. --> We need a consumer, authentications and write
operations must be forwarded to master.
If we choose the second use case, both the caching and request
forwarding must be implemented. I suppose that there shouldn't be big
problem to decide during the installation to turn the caching off by
some option like '-no-chaching' so that the consumer could be used for
the third use case as well.
Can you please now create a set usage scenarios for the 2) and 3).
User logs in and he is in cache, he is not in cache, he is redirected
and data is cached, he failed and account lockout data is updated
locally or on the other server? Admin tries to perform and IPA command
or ldapmodify command - what happens?
Can those work flows be spelled out in details for caching and non use
cases?
I'll start with usage scenario for 3), it's shorter:
All write operations and authentication requests are forwarded to the master
Operations when connection is OK:
----------------------------------------------
read -- local
write-forwarding to master
authentication-forwarding to master
Operations when connection is BROKEN:
-----------------------------------------------------
read-local (only until ticket expires)
write-not available
authentication-not available
Usage scenario for 2):
USER'S operations when connection is OK:
-------------------------------------------------------
read data -> local
write data -> forwarding to master
authentication:
-credentials cached -- authenticate against credentials in local cache
-on failure: log failure locally, update data
about failures only on lock-down of account
-credentials not cached -- forward request to master, on success cache
the credentials
USER'S operations when connection is BROKEN:
--------------------------------------------------------------
read data -> local
write data -> not available
authentication:
-credentials cached -- authenticate against credentials in local cache
-on failure: log failure locally, on
lock-down lock account locally and update information to master when the
connection is back on
-credentials not cached -- deny access -- not possible to authenticate user
ad ADMIN'S -- I suppose that admin's credentials should not be cached --
it doesn't make much sense because all the operations, he's permitted to
do, could be executed on master server only
ADMIN'S operations when connection is OK:
---------------------------------------------------------
read - local
write - forwarding to master
authentication - forwarding to master
ADMIN'S operations when connection is BROKEN:
----------------------------------------------------------------
read-only operations until valid ticket expires
write - not available
authentication - not available
--
Regards,
Ondrej Hamada
FreeIPA team
jabber: oh...@jabbim.cz
IRC: ohamada
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