Roles of zookeeper in solr cloud

Question

I am new to SolrCloud(4.X), Can anybody explain in detail about roles and responsibility of zookeeper in SolrCloud? Also how does zookeper work in regards to search/add request to Solr?

Answer 1

Zookeepers are a central repository for SolrCloud configuration. You can consider it as a distributed filesystem which can be accessed by all Solr nodes in the cluster. So if you change any config file you just need to inform or upload it to Zookeeper and not on every node in the cluster.

One more important responsibility of Zookeeper is to keep an eye on the state of all Solr nodes in the cluster. If any node goes down and a search request comes in for that node, Zookeeper routes it to an alternative replica node.

When you are updating any document in SolrCloud, it is zookeeper who delegates your update request to the appropriate node in the cloud holding the document

For in depth details you should be reading this, https://cwiki.apache.org/confluence/display/ZOOKEEPER/ProjectDescription