1.4. Creating Service Principals and Keytab Files for HDP

Each service in HDP must have its own principal. As services do not login with a password to acquire their tickets, their principal's authentication credentials are stored in a keytab file, which is extracted from the Kerberos database and stored locally with the service principal. First you must create the principal, using mandatory naming conventions. Then you must create the keytab file with that principal's information and copy the file to the keytab directory on the appropriate service host.

Create a service principal using the kadmin utility:

kadmin: addprinc -randkey $principal_name/$fully.qualified.domain.name@YOUR-REALM.COM

You must have a principal with administrative permissions to use this command. The randkey is used to generate the password.

Note that in the example each service principal's name has appended to it the fully qualified domain name of the host on which it is running. This is to provide a unique principal name for services that run on multiple hosts, like DataNodes and TaskTrackers.

The addition of the hostname serves to distinguish, for example, a request from DataNode A from a request from DataNode B. This is important for two reasons:

If the Kerberos credentials for one DataNode are compromised, it does not automatically lead to all DataNodes being compromised
If multiple DataNodes have exactly the same principal and are simultaneously connecting to the NameNode, and if the Kerberos authenticator being sent happens to have same timestamp, then the authentication would be rejected as a replay request.

The $principal_name part of the name must match the values in the table below:

Note that the NameNode, Secondary NameNode, and Oozie require two principals each.

Table 13.1. Service Principal Names

Service Name	Mandatory Principal Name
NameNode	`nn` AND `HTTP`
Secondary NameNode	`nn` AND `HTTP`
JobTracker	`jt`
TaskTracker	`tt`
DataNode	`dn`
HBase Master	`hbase`
HBase RegionServer	`hbase`
ZooKeeper	`zookeeper`
HCatalog Server	`hcat`
Oozie	`oozie` and `HTTP`
WebHCat (Templeton)	`HTTP`

For example: To create the principal for a DataNode service, issue this command:

kadmin: addprinc -randkey dn/$DataNode-Host@EXAMPLE.COM

Extract the related keytab file and place it in the keytab directory (by default /etc/krb5.keytab) of the appropriate respective components:

kadmin: xst -norandkey -k $keytab_file_name $principal_name/fully.qualified.domain.name

You must use the mandatory names for the $keytab_file_name; variable shown in this table.

Table 13.2. Service Keytab File Names

Service Name	Mandatory Keytab File Name
NameNode	`nn.service.keytab` AND `spnego.service.keytab`
Secondary NameNode	`nn.service.keytab` AND `spnego.service.keytab`
JobTracker	`jt.service.keytab`
TaskTracker	`tt.service.keytab`
DataNode	`dn.service.keytab`
HBase Master	`hbase.service.keytab`
HBase RegionServer	`hbase.service.keytab`
ZooKeeper	`zookeeper.service.keytab`
HCatalog Server	`hcat.service.keytab`
Oozie	`oozie.service.keytab` AND `spnego.service.keytab`
Templeton	`spnego.service.keytab`

For example: To create the keytab files for the NameNode, issue these commands:

 kadmin: xst -k nn.service.keytab nn/<namenode-host> 
kadmin: xst -k spnego.service.keytab HTTP/<namenode-host>

When you have created the keytab files, copy them to the keytab directory of the respective service hosts.

Set appropriate permissions for the keytabs.

Secure all the keytabs. Execute the following command on all the hosts on your cluster:
```
chown -R root:hadoop /etc/security/keytabs
chmod -R g+rX,o= /etc/security/keytabs
```

On the NameNode, execute the following command:

chown hdfs:hadoop /etc/security/keytabs/nn.service.keytab 
chmod 400 /etc/security/keytabs/nn.service.keytab

Execute the following command on all the slave nodes:

chown hdfs:hadoop /etc/security/keytabs/dn.service.keytab 
chown mapred:hadoop /etc/security/keytabs/tt.service.keytab 
chmod 400 /etc/security/keytabs/*.service.keytab

Verify that the correct keytab files and principals are associated with the correct service using the klist command. For example, on the NameNode:
```
klist –k -t /etc/security/nn.service.keytab
```
Do this on each respective service in your cluster.

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