[SOLR-8666] Add header to SearchHandler to indicate whether solr is connection to zk

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 6.0
• Assignee: Dennis Gove
• Reporter: Keith Laban
• Created: 09/Feb/16 22:24
• Updated: 09/May/16 18:55
• Resolved: 20/Mar/16 15:16

Description

Currently solr update requests error out if a zookeeper check fails, however SearchHandler does not do these checks. As a result, if a request is sent to a node which should be part of a SolrCloud but is not connected to zookeeper and thinks that its Active, it's possible the response is composed of stale data.

The purpose of this header is to allow the client to decide whether or not the result data should be considered valid.

This patch also returns the zkConnected header in the ping handler to allow external health checks to use this information.

See SOLR-8599 for an example of when this situation can arise.