Review cache replicas and clustering

[megian]

Context

A quorum is not required according the Keycloak user group. However an odd number might have benefits on split brain scenarios.

A cache owner default value of two is the default configuration. "Each distributed cache has two owners per default, which means that two nodes have a copy of the specific cache entries... When both owner nodes are offline, all data is lost...."

sh-4.4$ grep owners /opt/keycloak/conf/cache-ispn.xml
        <distributed-cache name="sessions" owners="2">
        <distributed-cache name="authenticationSessions" owners="2">
        <distributed-cache name="offlineSessions" owners="2">
        <distributed-cache name="clientSessions" owners="2">
        <distributed-cache name="offlineClientSessions" owners="2">
        <distributed-cache name="loginFailures" owners="2">
        <distributed-cache name="actionTokens" owners="2">

An individual cache-ispn.xml can be configured KC_CACHE_CONFIG_FILE changing the hole Infinispan configuration including the owner number.

So check if there would be benefits of having more cache replicas for certain cluster configurations.

Reference:

• Running fault-tolerant Keycloak with Infinispan in Kubernetes
• Comparison of cache modes
• Infinispan: Handling-cluster-partitions

Alternatives

Just support a two Keycloak instance clustering