This is a short and simple example on how to build a proper Keycloak cluster, using DNS_PING as discovery protocol and an NGINX server as reverse proxy.
If you prefer to use JDBC_PING, see @xgp's example gist here: https://gist.github.com/xgp/768eea11f92806b9c83f95902f7f8f80
Please see also my video about Keycloak Clustering: http://www.youtube.com/watch?v=P96VQkBBNxU
NOTE: The video covers JDBC_PING protocol and uses the legacy Keycloak Wildfly distribution!