High-Availability of Keycloak across remote sites
I’ve been looking into Keycloak as an on-prem IAM and SSO solution for my company. One thing that I’m unclear on from reading the documentation is if Keycloak’s clustered mode can handle our requirements for instance federation across sites.
We have some remote manned sites that occasionally run critical telemetry-gathering processes. Our AD domain is replicated to those sites.
The issue is that there is a single internet link to the sites. If we had keycloak at the main office, and the internet link went down for a day, any software at the remote site that relies on keycloak to authenticate wouldn’t work (which would be a big problem).
Can we set up Keycloak in a cluster mode (ie, putting an instance at each site), so that if this link went out, remote users are able to connect to their local instance automatically and authenticate with local apps? What happens when the connection is restored and the databases are out of sync - does keycloak automatically repair this?
In general answer is "yes", you can setup two keycloak instances in different locations, and link them with each other via cluster (under the hood it would be infinispan cache replication). But it depends on details of your infrastructure.
Main goal of Keycloak cluster is to perform sessions cache replication between nodes. So in simplest case you can setup two nodes that looks to same DB instance, and when first node goes down second would handle whole job, but if DB also goes down second node would be useless. In such case each site should have both separate Keycloak node and DB replica (how to achieve DB replication is out of scope of this topic). Third option is to use multitenancy feature of keycloak application adapter, in that case you secure application by two separate Keycloak instances, that know nothing about each other.
Try to start from this documentation article: https://www.keycloak.org/docs/latest/server_installation/index.html#crossdc-mode