What is the most important change in 4.x version of Apache Solr? I think there are many of them but Solr Cloud is definitely something that changed a lot in Solr architecture. Until now, bigger installations suffered from single point of failure (SPOF) – there was only the one master server and when this server was going down, the whole cluster lose the ability to receive new data. Solr Cloud changed this behavior. In this article we will setup a new SolrCloud cluster from the scratch and we will see how it work.