Secure configs with ZooKeeper ACLs and Ranger

You can restrict access to configuration sets by setting ZooKeeper ACLs on all znodes under and including /solr and using Ranger to control access to the ConfigSets API.

Ranger requires Kerberos authentication.

The solrctl instancedir command interacts directly with ZooKeeper, and therefore cannot be protected by Ranger. Because the solrctl config command is a wrapper script for the ConfigSets API, it can be protected by Ranger.

To force users to use the ConfigSets API, you must set all ZooKeeper znodes under and including /solr to read-only (except for the solr user).

After completing these steps, you cannot run commands such as solrctl instancedir --create or solrctl instancedir --delete without first authenticating as the solr@EXAMPLE.COM super user principal. Unauthenticated users can still run solrctl instancedir --list and solrctl instancedir --get, because those commands only perform read operations against ZooKeeper.

Create a jaas.conf file containing the following:

Client {
           com.sun.security.auth.module.Krb5LoginModule required
           useKeyTab=false
           useTicketCache=true
           principal="solr@EXAMPLE.COM";
           };

Replace EXAMPLE.COM with your Kerberos realm name.

Set the LOG4J_PROPS environment variable to a log4j.properties file:
```
export LOG4J_PROPS=/etc/zookeeper/conf/log4j.properties
```

Set the ZKCLI_JVM_FLAGS environment variable:

export ZKCLI_JVM_FLAGS="-Djava.security.auth.login.config=/path/to/jaas.conf \
             -DzkACLProvider=org.apache.solr.common.cloud.SaslZkACLProvider \
             -Droot.logger=INFO,console"

Authenticate as the solr user:
```
kinit solr@EXAMPLE.COM
```
Replace EXAMPLE.COM with your Kerberos realm name.
Run the zkcli.sh script as follows:
```
/opt/cloudera/parcels/CDH/lib/solr/bin/zkcli.sh -zkhost zk01.example.com:2181 -cmd updateacls /solr
```
Replace zk01.example.com with the hostname of a ZooKeeper server.