[keycloak-user] Is quorum needed in Keycloak Standalone Clustered Configuration?

[Sebastian Laskawiec]

On Thu, Aug 8, 2019 at 1:26 PM Roman Ok <warrior7089 at gmail.com> wrote:

> Sorry, i'm sending this again as my last post was posted without text for
> some unknown reason:
>
> Should an Keycloak deployments configured in Standalone Clustered
> Configuration have odd number of nodes to ensure quorum?
>

No, Keycloak uses Infinispan for caching and Infinispan uses JGroups for
clustering. JGroups doesn't need consensus.


>
> It's stated that Keycloak is built on top of the WildFly application
> server and its sub-projects like Infinispan (for caching) and Hibernate
> (for persistence).
>
> Keycloak recommends to look in WildFly Documentation and High Availability
> Guide.
>
> If understood correctly Standalone Clustered Configuration allows session
> replication or transmission of SSO contexts around the cluster.
>
> I don't understand though if odd number of Keycloak nodes is required so
> that there will be quorum.
>

No it is not strictly required. As in almost all distributed systems,
having odd number of nodes helps recovering from Split Brain scenarios.


>
> Singleton subsystem states
>
> 10.1.3. Quorum Network partitions are particularly problematic for
> singleton services, since they can trigger multiple singleton providers for
> the same service to run at the same time. To defend against this scenario,
> a singleton policy may define a quorum that requires a minimum number of
> nodes to be present before a singleton provider election can take place. A
> typical deployment scenario uses a quorum of N/2 + 1, where N is the
> anticipated cluster size. This value can be updated at runtime, and will
> immediately affect any active singleton services. e.g.
>
> Is it somehow related to Keycloak and its Standalone Clustered
> Configuration?
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