Hey guys, During our weekly sync meeting, Stian asked me to look into different options for clustering in Keycloak server. This topic has quite hot with the context of our Docker image (see the proposed community contributions [1][2][3]). Since we are based on WF 13, which uses JGroups 4.0.11 and has KUBE_PING in its modules, we have a couple of options how to do it. Before discussing different implementations, let me quickly go through the requirements: - We need a configuration stack that works for on-prem and cloud deployments with OpenShift as our primary target. - The configuration should be automatic (if it's possible). E.g. if we discover that Keycloak is running in the container, we should use proper discovery protocol. - There needs to be a way to override the discovery protocol manually. With those requirements in mind, we have a couple of implementation options on the table: 1. Add more stacks to the configuration, e.g. openshift, azure or gcp. Then we use the standard `-Djboss.default.jgroups.stack=<stack>` configuration switch. 2. Provide more standalone-*.xml configuration files, e.g. standalone-ha.xml (for on-prem) or standalone-cloud.xml. 3. Add protocols dynamically using CLI. A similar approach to what we did for the Data Grid Cache Service [4]. 4. Use MULTI_PING protocols [5][6], with multiple discovery protocols on the same stack. This will include MPING (for multicasting), KUBE_PING (if we can access Kubernetes API), DNS_PING (if Pods are governed by a Service). Option #1 and #2 is somewhat similar to what we did for Infinispan [7]. It works quite well but the configuration grows quite quickly and most of the protocols (apart from discovery) are duplicated. On the other hand, having separate configuration pieces for each use case is very flexible. Having in mind that AWS cuts TCP connections, using FD_SOCK might lead to false suspicions but on GCP for the instance, FD_SOCK works quite nicely. The CLI option (#3), is also very flexible and probably should be implemented only in our Docker image. This somehow follows the convention we already started with different CLI files for different DBs [8]. Option #4 is brand new (implemented in JGroups 4.0.8; we have 4.0.11 as you probably recall). It has been specifically designed for this kind of use cases where we want to gather discovery data from multiple places. Using this way, we should end up with two stacks in standalone-ha.xml file - UDP and TCP. I honestly need to say, that my heart goes for options #4. However, as far as I know it hasn't been battle tested and we might get some surprises. All other options are not as elegant as option #4 but they are used somewhere in other projects. They are much safer options but they will add some maintenance burden on our shoulders. What would you suggest guys? What do you think about all this? @Rado, @Paul, @Tristan - Do you have any plans regarding this piece in Wildfly or Infinispan? Thanks, Sebastian [1] https://github.com/jboss-dockerfiles/keycloak/pull/96 [2] https://github.com/jboss-dockerfiles/keycloak/pull/100 [3] https://github.com/jboss-dockerfiles/keycloak/pull/116 [4] https://github.com/jboss-container-images/datagrid-7-image/blob/datagrid-... [5] http://www.jgroups.org/manual4/index.html#_multi_ping [6] https://issues.jboss.org/browse/JGRP-2224 [7] https://github.com/infinispan/infinispan/tree/master/server/integration/j... [8] https://github.com/jboss-dockerfiles/keycloak/tree/master/server/tools/cl...