Hello everyone, We are running a SolrCloud cluster with ZooKeeper. This SolrCloud cluster is down most of the time (backup environment) but the ZooKeeper instances are always up so that we can easily update configuration.
This has been working fine for a long time with Solr 6.4.0 then 6.6.0, but since upgrading to 7.2.1, we ran into an issue where Solr ignores aliases.json stored in ZooKeeper. Steps to reproduce the problem: 1/ SolrCloud cluster is down 2/ Direct update of aliases.json file in ZooKeeper with Solr ZkCLI *without using Collections API* : java ... org.apache.solr.cloud.ZkCLI -zkhost ... -cmd clear /aliases.json java ... org.apache.solr.cloud.ZkCLI -zkhost ... -cmd put /aliases.json "new content" 3/ SolrCloud cluster is started => aliases.json not taken into account Digging a bit in the code, what is actually causing the issue is that, when starting, Solr now checks for the metadata of the aliases.json file and if the version metadata from ZooKeeper is lower or equal to local version, it keeps the local version. When it starts, Solr has a local version of 0 for the aliases but ZooKeeper also has a version of 0 of the file because we just recreated it. So Solr ignores ZooKeeper configuration and never has a chance to load aliases. Relevant parts of Solr code are: - https://github.com/apache/lucene-solr/blob/branch_7_2/solr/solrj/src/java/org/apache/solr/common/cloud/ZkStateReader.java : line 4562 : method setIfNewer - https://github.com/apache/lucene-solr/blob/branch_7_2/solr/solrj/src/java/org/apache/solr/common/cloud/Aliases.java : line 45 : the "empty" Aliases object with default version 0 Obviously, a workaround is to force ZooKeeper to have a version greater than 0 for aliases.json file (for instance by not clearing the file and just overwriting it again and again). But we were wondering, is this the intended behavior for Solr ? Thanks for reading, Gaël
