The documentation presented here: https://cwiki.apache.org/confluence/display/solr/ZooKeeper+Access+Control
details the process of securing Solr content in ZooKeeper using ACLs. In the example usages, it is mentioned that access to zkcli can be restricted by adding credentials to the zkcli.sh script in addition to adding the appropriate classnames to solr.xml. With the scripts in zkcli.sh, another machine should not be able to read or write from the host ZK without the necessary credentials. At this time, machines are able to read/write from the host ZK with or without these credentials.