Kerberizing Embedded ZooKeeper Server

The krb5.conf file on the systems with the embedded zookeeper servers should be identical to the one on the system where the krb5kdc service is running. When using the embedded ZooKeeper server, we may choose to secure the server by using Kerberos. All nodes configured to launch an embedded ZooKeeper and using Kerberos should follow these steps. When using the embedded ZooKeeper server, we may choose to secure the server by using Kerberos. All nodes configured to launch an embedded ZooKeeper and using Kerberos should follow these steps.

In order to use Kerberos, we first need to generate a Kerberos Principal for our ZooKeeper servers. The following command is run on the server where the krb5kdc service is running. This is accomplished via the kadmin tool:

         kadmin: addprinc "zookeeper/myHost.example.com@EXAMPLE.COM"
      

Here, we are creating a Principal with the primary zookeeper/myHost.example.com, using the realm EXAMPLE.COM. We need to use a Principal whose name is <service name>/<instance name>. In this case, the service is zookeeper and the instance name is myHost.example.com (the fully qualified name of our host).

Next, we will need to create a KeyTab for this Principal, this command is run on the server with the NiFi instance with an embedded zookeeper server:

         kadmin: xst -k zookeeper-server.keytab zookeeper/myHost.example.com@EXAMPLE.COM
      

This will create a file in the current directory named zookeeper-server.keytab. We can now copy that file into the $NIFI_HOME/conf/ directory. We should ensure that only the user that will be running NiFi is allowed to read this file.

We will need to repeat the above steps for each of the instances of NiFi that will be running the embedded ZooKeeper server, being sure to replace myHost.example.com with myHost2.example.com, or whatever fully qualified hostname the ZooKeeper server will be run on.

Now that we have our KeyTab for each of the servers that will be running NiFi, we will need to configure NiFi's embedded ZooKeeper server to use this configuration. ZooKeeper uses the Java Authentication and Authorization Service (JAAS), so we need to create a JAAS-compatible file In the $NIFI_HOME/conf/ directory, create a file named zookeeper-jaas.conf (this file will already exist if the Client has already been configured to authenticate via Kerberos. That's okay, just add to the file). We will add to this file, the following snippet:

         Server {
  com.sun.security.auth.module.Krb5LoginModule required
  useKeyTab=true
  keyTab="./conf/zookeeper-server.keytab"
  storeKey=true
  useTicketCache=false
  principal="zookeeper/myHost.example.com@EXAMPLE.COM";
};
      

Be sure to replace the value of principal above with the appropriate Principal, including the fully qualified domain name of the server.

Next, we need to tell NiFi to use this as our JAAS configuration. This is done by setting a JVM System Property, so we will edit the conf/bootstrap.conf file. If the Client has already been configured to use Kerberos, this is not necessary, as it was done above. Otherwise, we will add the following line to our bootstrap.conf file:

         java.arg.15=-Djava.security.auth.login.config=./conf/zookeeper-jaas.conf
      

Note: this additional line in the file doesn't have to be number 15, it just has to be added to the bootstrap.conf file, use whatever number is appropriate for your configuration.

We will want to initialize our Kerberos ticket by running the following command:

         kinit -kt zookeeper-server.keytab "zookeeper/myHost.example.com@EXAMPLE.COM"
      

Again, be sure to replace the Principal with the appropriate value, including your realm and your fully qualified hostname.

Finally, we need to tell the Kerberos server to use the SASL Authentication Provider. To do this, we edit the $NIFI_HOME/conf/zookeeper.properties file and add the following lines:

         authProvider.1=org.apache.zookeeper.server.auth.SASLAuthenticationProvider
kerberos.removeHostFromPrincipal=true
kerberos.removeRealmFromPrincipal=true
jaasLoginRenew=3600000
requireClientAuthScheme=sasl
      

The kerberos.removeHostFromPrincipal and the kerberos.removeRealmFromPrincipal properties are used to normalize the user principal name before comparing an identity to acls applied on a Znode. By default the full principal is used however setting the removeHostFromPrincipal and removeRealmFromPrincipal kerberos properties to true will instruct Zookeeper to remove the host and the realm from the logged in user's identity for comparison. In cases where NiFi nodes (within the same cluster) use principals that have different host(s)/realm(s) values, these kerberos properties can be configured to ensure that the nodes' identity will be normalized and that the nodes will have appropriate access to shared Znodes in Zookeeper.

The last line is optional but specifies that clients MUST use Kerberos to communicate with our ZooKeeper instance.

Now, we can start NiFi, and the embedded ZooKeeper server will use Kerberos as the authentication mechanism.