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Configure MongoDB with Kerberos Authentication on Linux

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Overview

MongoDB Enterprise supports authentication using a Kerberos service. Kerberos is an industry standard authentication protocol for large client/server systems. MongoDB Enterprise only supports the MIT implementation of Kerberos.

Prerequisites

To verify that you are using MongoDB Enterprise, pass the --version command line option to the mongod or mongos:

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mongod --version

In the output from this command, look for the string modules: subscription or modules: enterprise to confirm you are using the MongoDB Enterprise binaries.

For replica sets and sharded clusters, ensure that your configuration uses fully qualified domain names (FQDN) rather than IP addresses or unqualified hostnames. You must use the FQDN for GSSAPI to correctly resolve the Kerberos realms and allow you to connect.

Setting up and configuring a Kerberos deployment is beyond the scope of this document. Please refer to the MIT Kerberos documentation or your operating system documentation for information on how to configure a Kerberos deployment.

In order to use MongoDB with Kerberos, a Kerberos service principal for each mongod and mongos instance in your MongoDB deployment must be added to the Kerberos database. You can add the service principal by running a command similar to the following on your KDC:

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kadmin.local addprinc mongodb/[email protected]

On each system running mongod or mongos, a keytab file must be created for the respective service principal. You can create the keytab file by running a command similar to the following on the system running mongod or mongos:

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kadmin.local ktadd mongodb/[email protected]

Procedure

The following procedure outlines the steps to add a Kerberos user principal to MongoDB, configure a standalone mongod instance for Kerberos support, and connect using the mongo shell and authenticate the user principal.

1

Start mongod without Kerberos.

For the initial addition of Kerberos users, start mongod without Kerberos support.

If a Kerberos user is already in MongoDB and has the privileges required to create a user, you can start mongod with Kerberos support.

Include additional settings as appropriate to your deployment.

Note

Starting in MongoDB 3.6, mongod and mongos bind to localhost by default. If the members of your deployment are run on different hosts or if you wish remote clients to connect to your deployment, you must specify --bind_ip or net.bindIp. For more information, see Localhost Binding Compatibility Changes.

2

Connect to mongod.

Connect via the mongo shell to the mongod instance. If mongod has --auth enabled, ensure you connect with the privileges required to create a user.

3

Add Kerberos Principal(s) to MongoDB.

Add a Kerberos principal, <username>@<KERBEROS REALM> or <username>/<instance>@<KERBEROS REALM>, to MongoDB in the $external database. Specify the Kerberos realm in all uppercase. The $external database allows mongod to consult an external source (e.g. Kerberos) to authenticate. To specify the user’s privileges, assign roles to the user.

Changed in version 3.6.3: To use sessions with $external authentication users (i.e. Kerberos, LDAP, x.509 users), the usernames cannot be greater than 10k bytes.

The following example adds the Kerberos principal application/reporting@EXAMPLE.NET with read-only access to the records database:

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use $external
db.createUser(
   {
     user: "application/[email protected]",
     roles: [ { role: "read", db: "records" } ]
   }
)

Add additional principals as needed. For every user you want to authenticate using Kerberos, you must create a corresponding user in MongoDB. For more information about creating and managing users, see User Management Commands.

4

Start mongod with Kerberos support.

To start mongod with Kerberos support, set the environmental variable KRB5_KTNAME to the path of the keytab file and the mongod parameter authenticationMechanisms to GSSAPI in the following form:

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env KRB5_KTNAME=<path to keytab file> \
mongod \
--setParameter authenticationMechanisms=GSSAPI \
<additional mongod options>

Include additional options as required for your configuration. For instance, if you wish remote clients to connect to your deployment or your deployment members are run on different hosts, specify the --bind_ip. For more information, see Localhost Binding Compatibility Changes.

For example, the following starts a standalone mongod instance with Kerberos support:

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env KRB5_KTNAME=/opt/mongodb/mongod.keytab \
/opt/mongodb/bin/mongod --auth \
--setParameter authenticationMechanisms=GSSAPI \
--dbpath /opt/mongodb/data --bind_ip localhost,<hostname(s)|ip address(es)>

The path to your mongod as well as your keytab file may differ. The keytab file must be only accessible to the owner of the mongod process.

With the official .deb or .rpm packages, you can set the KRB5_KTNAME in a environment settings file. See KRB5_KTNAME for details.

5

Connect mongo shell to mongod and authenticate.

Connect the mongo shell client as the Kerberos principal application/reporting@EXAMPLE.NET. Before connecting, you must have used Kerberos’s kinit program to get credentials for application/reporting@EXAMPLE.NET.

You can connect and authenticate from the command line.

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mongo --host hostname.example.net --authenticationMechanism=GSSAPI --authenticationDatabase='$external' --username application/[email protected]

If you are connecting to a system whose hostname matches the Kerberos name, ensure that you specify the fully qualified domain name (FQDN) for the --host option, rather than an IP address or unqualified hostname.

If you are connecting to a system whose hostname does not match the Kerberos name, use --gssapiHostName to specify the Kerberos FQDN that it responds to.

Alternatively, you can first connect mongo to the mongod, and then from the mongo shell, use the db.auth() method to authenticate in the $external database.

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use $external
db.auth( { mechanism: "GSSAPI", user: "application/[email protected]" } )

Additional Considerations

KRB5_KTNAME

If you installed MongoDB Enterprise using one of the official .deb or .rpm packages, and you use the included init/upstart scripts to control the mongod instance, you can set the KR5_KTNAME variable in the default environment settings file instead of setting the variable each time.

For .rpm packages, the default environment settings file is /etc/sysconfig/mongod.

For .deb packages, the file is /etc/default/mongodb.

Set the KRB5_KTNAME value in a line that resembles the following:

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export KRB5_KTNAME="<path to keytab>"

Configure mongos for Kerberos

To start mongos with Kerberos support, set the environmental variable KRB5_KTNAME to the path of its keytab file and the mongos parameter authenticationMechanisms to GSSAPI in the following form:

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env KRB5_KTNAME=<path to keytab file> \
mongos \
--setParameter authenticationMechanisms=GSSAPI \
<additional mongos options>

Include additional options as required for your configuration. For instance, if you wish remote clients to connect to your deployment or your deployment members are run on different hosts, specify the --bind_ip. For more information, see Localhost Binding Compatibility Changes.

For example, the following starts a mongos instance with Kerberos support:

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env KRB5_KTNAME=/opt/mongodb/mongos.keytab \
mongos \
--setParameter authenticationMechanisms=GSSAPI \
--configdb shard0.example.net, shard1.example.net,shard2.example.net \
--keyFile /opt/mongodb/mongos.keyfile \
--bind_ip localhost,<hostname(s)|ip address(es)>

The path to your mongos as well as your keytab file may differ. The keytab file must be only accessible to the owner of the mongos process.

Modify or include any additional mongos options as required for your configuration. For example, instead of using --keyFile for internal authentication of sharded cluster members, you can use x.509 member authentication instead.

Use a Config File

To configure mongod or mongos for Kerberos support using a configuration file, specify the authenticationMechanisms setting in the configuration file.

If using the YAML configuration file format:

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setParameter:
   authenticationMechanisms: GSSAPI

Include additional options as required for your configuration. For instance, if you wish remote clients to connect to your deployment or your deployment members are run on different hosts, specify the net.bindIp setting. For more information, see Localhost Binding Compatibility Changes.

For example, if /opt/mongodb/mongod.conf contains the following configuration settings for a standalone mongod:

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security:
   authorization: enabled
setParameter:
   authenticationMechanisms: GSSAPI
storage:
   dbPath: /opt/mongodb/data
net:
   bindIp: localhost,<hostname(s)|ip address(es)>

To start mongod with Kerberos support, use the following form:

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env KRB5_KTNAME=/opt/mongodb/mongod.keytab \
/opt/mongodb/bin/mongod --config /opt/mongodb/mongod.conf

The path to your mongod, keytab file, and configuration file may differ. The keytab file must be only accessible to the owner of the mongod process.

Troubleshoot Kerberos Setup for MongoDB

If you encounter problems when starting mongod or mongos with Kerberos authentication, see Troubleshoot Kerberos Authentication.

Incorporate Additional Authentication Mechanisms

Kerberos authentication (GSSAPI (Kerberos)) can work alongside:

  • MongoDB’s SCRAM authentication mechanism:
  • MongoDB’s authentication mechanism for LDAP:
  • MongoDB’s authentication mechanism for x.509:

Specify the mechanisms as follows:

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--setParameter authenticationMechanisms=GSSAPI,SCRAM-SHA-256

Only add the other mechanisms if in use. This parameter setting does not affect MongoDB’s internal authentication of cluster members.

Testing and Verification

After completing the configuration steps, you can validate your configuration with the mongokerberos tool.

Introduced alongside MongoDB 4.4, mongokerberos provides a convenient method to verify your platform’s Kerberos configuration for use with MongoDB, and to test that Kerberos authentication from a MongoDB client works as expected. See the mongokerberos documentation for more information.

mongokerberos is available in MongoDB Enterprise only.

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