[keycloak-dev] Slight refactoring of InfinispanUserSessionProvider

Tue May 16 04:40:39 EDT 2017

On 16/05/17 09:38, Schuster Sebastian (INST/ESY1) wrote:
> Hi Marek,
>
> You mentioned in your proposed solution that " The changes may not be guaranteed in same order in every DC". Wouldn't that be a problem as it leads to inconsistent data in different data centers?
I was thinking about that and ATM I can't see the scenario when it is a 
problem with respect to our business logic related to userSession model.

For example it can happen that there is request1 for add client 
"client1" in dc1. And at the same time request2 for add "client2" in 
dc2.  So it may happen that request1 will add "client1" to the 
userSession and send the message to dc2 for add "client1" . At the same 
time request2 will add "client2" to the userSession in dc2 and send the 
message to dc1 for add "client1" . After some time, both DCs will 
receive the message from the other DC and both will update their client 
list to be ["client1", "client2"] .

Important is, that there won't be lost update (which can easily happen 
now).

There are various corner cases (eg. DC will receive the message about 
update of userSession, which was already logged-out/removed in this DC 
etc), but all of those can be handled IMO.

One special thing is code-to-token request as it can happen very quickly 
after the userSession is created. And it can be processed on different 
DC then the one when userSession was created. So my current thinking is 
to not lookup userSession in code-to-token request at all, but instead 
rely on the information in the code, which will itself be JWT and will 
encapsulate all the informations to be put into the token itself. I will 
likely send another email about that..

I think that for the case when you want to ensure very consistent 
behaviour, you will be able to configure the channel between datacenters 
to be SYNC instead of ASYNC. However that will have performance penalty.

Marek
>
> Best regards,
> Sebastian
>
> P.S.: If I recall correctly, Infinispan does not support a "serializable" isolation level preventing lost updates, so even if Keycloak used the transaction API, it would not help...
>
> Mit freundlichen Grüßen / Best regards
>
>   Sebastian Schuster
>
> Engineering and Support (INST/ESY1)
> Bosch Software Innovations GmbH | Schöneberger Ufer 89-91 | 10785 Berlin | GERMANY | www.bosch-si.com
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>
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>
> -----Original Message-----
> From: keycloak-dev-bounces at lists.jboss.org [mailto:keycloak-dev-bounces at lists.jboss.org] On Behalf Of Marek Posolda
> Sent: Montag, 15. Mai 2017 18:25
> To: keycloak-dev at lists.jboss.org
> Subject: [keycloak-dev] Slight refactoring of InfinispanUserSessionProvider
>
> In today's call with Stian and Hynek, we discussed the possible refactoring of InfinispanUserSessionProvider to be reliable in cluster/cross-dc environment.
>
> Current implementation has tightly couple between the model
> (UserSessionAdapter) and underlying infinispan entity. For example when you call "userSessionModel.setLastSessionRefresh(123)" it directly delegates this call to infinispan entity and calls "entity.setLastSessionRefresh(123)" .
>
> Some issues with this approach:
>
> 1) Possibility of lost updates in cluster - It can happen that there are more concurrent requests updating same userSession. There is a fix by Bill [1], which adds the thread-safety to UserSessionEntity and fixes the issue in local environment. However in cluster with more nodes, it can still happen that there is "lost update". I've created the JIRA [2] for this with details. In shortcut, what can happen is, that there is
> request1 processed on node1 and request2 processed on node2 in parallel.
> Both requests read the sessionEntity and then both perform concurrent update and commits their transaction. Then the latter update wins and overwrites the first update as the state when it read the entity didn't yet contain the first update.
>
> 2) Rollback doesn't work correctly. Basically when we do this:
>
> {code}
> userSession.setLastSessionRefresh(123);
> session.transaction().rollback();
> {code}
>
> the keycloak transaction should be rolled-back and session in infinispan cache shouldn't be updated to lastSessionRefresh 123. However in current implementation, rollback doesn't work and entity is always updated in local environment and may be updated in cluster too (in case that calling node is the owner of session entity). That's because we are not using infinispan transaction API and calling "entity.setLastSessionRefresh(123)" directly updates the entity instance referenced by infinispan storage.
>
> 3) Cross-dc support with good performance
>
> Ideal is to fix all issues and ensure consistency, but have the same/similar performance at the same time and not introduce additional uneccessary locking.
>
>
> Possible solution:
>
> - Every change to UserSessionModel won't delegate directly to infinispan sessionEntity as it's now. Instead it will track the change through changelogs/events, which are saved locally in our infinispan transaction (eg. AddClientToSessionEvent, LastSessionRefreshUpdateEvent).
>
> - During Keycloak transaction commit are changelogs applied to sessionEntity. It may use atomic operation "cache.replace(key, oldValue, newValue)" and the pattern like this:
>
> {code}
> boolean replaced = false;
>
> while (!replaced) {
>       SessionEntity oldSession = cache.get("123");
>       // Will update session entity based on the changes tracked in infinispan transaction
>       SessionEntity updatedSession = applyChanges(oldSession);
>       replaced = cache.replace("123", oldSession, updatedSession); } {code}
>
> - In cross-dc environment are changes sent to another datacenter. That will receive changes (eg. AddClientToSessionEvent) and apply changes locally in the datacenter and update the sessionEntity in the infinispan. It shouldn't be a problem that those events are sent between datacenters through the asynchronous channel. The changes may not be guaranteed in same order in every DC, but all of them will be triggered and there won't be lost updates. So the cache "sessions" won't be directly replicated through the cross-dc, but instead the changes will be sent between datacenters.
>
> What do you think? Can you see some issues with this approach?
>
> Thanks,
> Marek
>
> [1] https://issues.jboss.org/browse/KEYCLOAK-4821
> [2] https://issues.jboss.org/browse/KEYCLOAK-4898
>
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