9.1. Coordinator Kerberos Authentication

The Presto coordinator can be configured to enable Kerberos authentication over HTTPS for clients, such as the Presto CLI, or the JDBC and ODBC drivers.

To enable Kerberos authentication for Presto, configuration changes are made on the Presto coordinator. No changes are required to the worker configuration; the worker nodes will continue to connect to the coordinator over unauthenticated HTTP.

Warning

Worker nodes cannot yet be configured to connect to the Presto coordinator using HTTPS or to authenticate with Kerberos. It is the administrator’s responsibility to enable unauthenticated access over HTTP for worker nodes and ensure unathenticated access is blocked for any node that is not a worker node. For nodes that are not worker nodes, block access to the Presto coordinator’s HTTP port.

Environment Configuration

Kerberos Services

You will need a Kerberos KDC running on a node that the Presto coordinator can reach over the network. The KDC is responsible for authenticating principals and issuing session keys that can be used with Kerberos-enabled services. KDCs typically run on port 88, which is the IANA-assigned port for Kerberos.

MIT Kerberos Configuration

Kerberos needs to be configured on the Presto coordinator. At a minimum, there needs to be a kdc entry in the [realms] section of the /etc/krb5.conf file. You may also want to include an admin_server entry and ensure that the Presto coordinator can reach the Kerberos admin server on port 749.

[realms]
  PRESTO.EXAMPLE.COM = {
    kdc = kdc.example.com
    admin_server = kdc.example.com
  }

[domain_realm]
  .presto.example.com = PRESTO.EXAMPLE.COM
  presto.example.com = PRESTO.EXAMPLE.COM

The complete documentation for krb5.conf is hosted by the MIT Kerberos Project. If you are using a different implementation of the Kerberos protocol, you will need to adapt the configuration to your environment.

Kerberos Principals and Keytab Files

The Presto coordinator needs a Kerberos principal, as do users who are going to connect to the Presto coordinator. You will need to create these users in Kerberos using kadmin.

In addition, the Presto coordinator needs a keytab file. After you create the principal, you can create the keytab file using kadmin

kadmin
> addprinc -randkey presto@EXAMPLE.COM
> addprinc -randkey presto/presto-coordinator.example.com@EXAMPLE.COM
> ktadd -k /etc/presto/presto.keytab presto@EXAMPLE.COM
> ktadd -k /etc/presto/presto.keytab presto/presto-coordinator.example.com@EXAMPLE.COM

Note

Running ktadd randomizes the principal’s keys. If you have just created the principal, this does not matter. If the principal already exists, and if existing users or services rely on being able to authenticate using a password or a keytab, use the -norandkey option to ktadd.

Java Cryptography Extension Policy Files

The Java Runtime Environment is shipped with policy files that limit the strengh of the cryptographic keys that can be used. Kerberos, by default, uses keys that are larger than those supported by the included policy files. There are two possible solutions to the problem:

  • Update the JCE policy files.
  • Configure Kerberos to use reduced-strength keys.

Of the two options, updating the JCE policy files is recommended. The JCE policy files can be downloaded from Oracle. Note that the JCE policy files vary based on the major version of Java you are running. Java 6 policy files will not work with Java 8, for example.

The Java 8 policy files are available here. Instructions for installing the policy files are included in a README file in the ZIP archive. You will need administrative access to install the policy files if you are installing them in a system JRE.

Java Keystore File for TLS

When using Kerberos authentication, access to the Presto coordinator should be through HTTPS. You can do it by creating a Java Keystore File for TLS on the coordinator.

System Access Control Plugin

A Presto coordinator with Kerberos enabled will probably need a System Access Control plugin to achieve the desired level of security.

Presto Coordinator Node Configuration

You must make the above changes to the environment prior to configuring the Presto coordinator to use Kerberos authentication and HTTPS. After making the following environment changes, you can make the changes to the Presto configuration files.

config.properties

Kerberos authentication is configured in the coordinator node’s config.properties file. The entries that need to be added are listed below.

http-server.authentication.type=KERBEROS

http.server.authentication.krb5.service-name=presto
http.server.authentication.krb5.keytab=/etc/presto/presto.keytab
http.authentication.krb5.config=/etc/krb5.conf

http-server.https.enabled=true
http-server.https.port=7778

http-server.https.keystore.path=/etc/presto_keystore.jks
http-server.https.keystore.key=keystore_password
Property Description
http-server.authentication.type Authentication type for the Presto coordinator. Must be set to KERBEROS.
http.server.authentication.krb5.service-name The Kerberos server name for the Presto coordinator. Must match the Kerberos principal.
http.server.authentication.krb5.keytab The location of the keytab that can be used to authenticate the Kerberos principal specified in http.server.authentication.krb5.service-name.
http.authentication.krb5.config The location of the Kerberos configuration file.
http-server.https.enabled Enables HTTPS access for the Presto coordinator. Should be set to true.
http-server.https.port HTTPS server port.
http-server.https.keystore.path The location of the Java Keystore file that will be used to secure TLS.
http-server.https.keystore.key The password for the keystore. This must match the password you specified when creating the keystore.

Note

Monitor CPU usage on the Presto coordinator after enabling HTTPS. Java will choose CPU-intensive cipher suites by default. If the CPU usage is unacceptably high after enabling HTTPS, you can configure Java to use specific cipher suites by setting the http-server.https.included-cipher property:

http-server.https.included-cipher=TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_128_CBC_SHA256

The Java documentation lists the supported cipher suites.

access-controls.properties

At a minimum, an access-control.properties file must contain an access-control.name property. All other configuration is specific for the implementation being configured. See System Access Control for details.

Troubleshooting

Getting Kerberos authentication working can be challenging. You can independently verify some of the configuration outside of Presto to help narrow your focus when trying to solve a problem.

Kerberos Verification

Ensure that you can connect to the KDC from the Presto coordinator using telnet.

$ telnet kdc.example.com 88

Verify that the keytab file can be used to successfully obtain a ticket using kinit and klist

$ kinit -kt /etc/presto/presto.keytab presto@EXAMPLE.COM
$ klist

Java Keystore File Verification

Verify the password for a keystore file and view its contents using Java Keystore File Verification

Additional Kerberos Debugging Information

You can enable additional Kerberos debugging information for the Presto coordinator process by adding the following lines to the Presto jvm.config file

-Dsun.security.krb5.debug=true
-Dlog.enable-console=true

-Dsun.security.krb5.debug=true enables Kerberos debugging output from the JRE Kerberos libraries. The debugging output goes to stdout, which Presto redirects to the logging system. -Dlog.enable-console=true enables output to stdout to appear in the logs.

The amount and usefulness of the information the Kerberos debugging output sends to the logs varies depending on where the authentication is failing. Exception messages and stack traces can also provide useful clues about the nature of the problem.