[SOLR-14389] Support dynamic reconfiguration of Zookeeper ensemble

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: SolrCloud
• Assignee: Unassigned
• Reporter: Jan Høydahl
• Created: 05/Apr/20 22:17
• Updated: 13/Apr/21 12:20

Description

Spinoff from SOLR-14371.

Zookeeper has got support for dynamic reconfiguration since v3.5 (See https://zookeeper.apache.org/doc/r3.6.0/zookeeperReconfig.html). But users need to actively start using it. Currently Solr treats the ZK_HOST var / -DzkHost sysprop as a static truth, and will only ever attempt to connect to the hosts originally included in the connection string.

This issue aims to implement "Rebalancing Client Connections" as described in last paragrah in above link. This will let sys admins extend or change their ensemble, and Solr nodes will update and re-balance, as long as at least one of the zk hosts are still in the static ZK_HOST list.

Issue Links

• duplicates: SOLR-13801 Solr webapp should query zookeeper for active hosts for zk >3.5