I'm currently getting the following error when starting Solr in cloud mode (bin/solr start -c) in master. Could be related to this ticket, but not sure.
2017-05-01 02:36:29.297 ERROR (main) [ ] o.a.s.c.SolrCore null:java.lang.IllegalArgumentException: clientPort is not set
Pretty sure this ^ is caused by the ZK upgrade. Reopening to address.
Prior to this issue, Solr did its own parsing of zoo.cfg, but after this issue, Solr delegates to ZK's QuorumPeerConfig.parseProperties() to do so. ZK's method (unlike Solr's previous parsing code) requires that clientPort be specified in zoo.cfg.
Solr's check for missing clientPort configuration (and setting to solrPort + 1000 if absent) is currently performed after parsing zoo.cfg. I have a patch I'm testing that moves supplying a default clientPort to before QuorumPeerConfig.parseProperties().