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Update Sharded Cluster to Keyfile Authentication

Overview

Enforcing access control on a sharded cluster requires configuring:

• Security between components of the cluster using Internal Authentication.
• Security between connecting clients and the cluster using Role-Based Access Control.

For this tutorial, each member of the sharded cluster must use the same internal authentication mechanism and settings. This means enforcing internal authentication on each mongos and mongod in the cluster.

The following tutorial uses a keyfile to enable internal authentication.

Enforcing internal authentication also enforces user access control. To connect to the replica set, clients like the mongo shell need to use a user account. See Access Control.

CloudManager and OpsManager

If Cloud Manager or Ops Manager is managing your deployment, internal authentication is automatically enforced.

To configure Access Control on a managed deployment, see: Configure Access Control for MongoDB Deployments in the Cloud Manager manual or in the Ops Manager manual.

Considerations

Tip

When possible, use a logical DNS hostname instead of an ip address, particularly when configuring replica set members or sharded cluster members. The use of logical DNS hostnames avoids configuration changes due to ip address changes.

IP Binding

Changed in version 3.6.

Starting with MongoDB 3.6, MongoDB binaries, mongod and mongos, bind to localhost by default. From MongoDB versions 2.6 to 3.4, only the binaries from the official MongoDB RPM (Red Hat, CentOS, Fedora Linux, and derivatives) and DEB (Debian, Ubuntu, and derivatives) packages would bind to localhost by default. To learn more about this change, see Localhost Binding Compatibility Changes.

Operating System

This tutorial primarily refers to the mongod process. Windows users should use the mongod.exe program instead.

Keyfile Security

Keyfiles are bare-minimum forms of security and are best suited for testing or development environments. For production environments we recommend using x.509 certificates.

Access Control

This tutorial covers creating the minimum number of administrative users on the admin database only. For the user authentication, the tutorial uses the default SCRAM authentication mechanism. Challenge-response security mechanisms are best suited for testing or development environments. For production environments, we recommend using x.509 certificates or LDAP Proxy Authentication (available for MongoDB Enterprise only) or Kerberos Authentication (available for MongoDB Enterprise only).

For details on creating users for specific authentication mechanism, refer to the specific authentication mechanism pages.

See ➤ Configure Role-Based Access Control for best practices for user creation and management.

Users

In general, to create users for a sharded clusters, connect to the mongos and add the sharded cluster users.

However, some maintenance operations require direct connections to specific shards in a sharded cluster. To perform these operations, you must connect directly to the shard and authenticate as a shard-local administrative user.

Shard-local users exist only in the specific shard and should only be used for shard-specific maintenance and configuration. You cannot connect to the mongos with shard-local users.

See the Users security documentation for more information.

Downtime

Upgrading a sharded cluster to enforce access control requires downtime.

Procedures

Enforce Keyfile Internal Authentication on Existing Sharded Cluster Deployment

1

Create a keyfile.

With keyfile authentication, each mongod or mongos instances in the sharded cluster uses the contents of the keyfile as the shared password for authenticating other members in the deployment. Only mongod or mongos instances with the correct keyfile can join the sharded cluster.

Note

Starting in MongoDB 4.2, keyfiles for internal membership authentication use YAML format to allow for multiple keys in a keyfile. The YAML format accepts content of:

• a single key string (same as in earlier versions),
• multiple key strings (each string must be enclosed in quotes), or
• sequence of key strings.

The YAML format is compatible with the existing single-key keyfiles that use the text file format.

A key’s length must be between 6 and 1024 characters and may only contain characters in the base64 set. All members of the sharded cluster must share at least one common key.

Note

On UNIX systems, the keyfile must not have group or world permissions. On Windows systems, keyfile permissions are not checked.

You can generate a keyfile using any method you choose. For example, the following operation uses openssl to generate a complex pseudo-random 1024 character string to use as a shared password. It then uses chmod to change file permissions to provide read permissions for the file owner only:

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openssl rand -base64 756 > <path-to-keyfile>
chmod 400 <path-to-keyfile>

See Keyfiles for additional details and requirements for using keyfiles.

2

Copy the keyfile to each component in the sharded cluster.

Every server hosting a mongod or mongos component of the sharded cluster must contain a copy of the keyfile.

Copy the keyfile to each server hosting the sharded cluster members. Ensure that the user running the mongod or mongos instances is the owner of the file and can access the keyfile.

Avoid storing the keyfile on storage mediums that can be easily disconnected from the hardware hosting the mongod or mongos instances, such as a USB drive or a network attached storage device.

3

Disable the Balancer.

Connect a mongo shell to a mongos.

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sh.stopBalancer()

The balancer may not stop immediately if a migration is in progress. The sh.stopBalancer() method blocks the shell until the balancer stops.

Starting in MongoDB 4.2, sh.stopBalancer() also disables auto-splitting for the sharded cluster.

Use sh.getBalancerState() to verify that the balancer has stopped.

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sh.getBalancerState()

Important

Do not proceed until the balancer has stopped running.

See Manage Sharded Cluster Balancer for tutorials on configuring sharded cluster balancer behavior.

4

Shut down all mongos instances for the sharded cluster.

Connect a mongo shell to each mongos and shut them down.

Use the db.shutdownServer() method on the admin database to safely shut down the mongos:

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db.getSiblingDB("admin").shutdownServer()

Repeat until all mongos instances in the cluster are offline.

Once this step is complete, all mongos instances in the cluster should be offline.

5

Shut down config server mongod instances.

Connect a mongo shell to each mongod in the config server deployment and shut them down.

For replica set config server deployments, shut down the primary member last.

Use the db.shutdownServer() method on the admin database to safely shut down the mongod:

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db.getSiblingDB("admin").shutdownServer()

Repeat until all config servers are offline.

6

Shut down shard replica set mongod instances.

For each shard replica set, connect a mongo shell to each mongod member in the replica set and shut them down. Shut down the primary member last.

Use the db.shutdownServer() method on the admin database to safely shut down the mongod:

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db.getSiblingDB("admin").shutdownServer()

Repeat this step for each shard replica set until all mongod instances in all shard replica sets are offline.

Once this step is complete, the entire sharded cluster should be offline.

7

Enforce Access Control on the Config Servers.

Start each mongod in the config server replica set. Include the keyFile setting. The keyFile setting enforces both Internal/Membership Authentication and Role-Based Access Control.

You can specify the mongod settings either via a configuration file or the command line.

Configuration File

If using a configuration file, for a config server replica set, set security.keyFile to the keyfile’s path, sharding.clusterRole to configsvr, and replication.replSetName to the name of the config server replica set.

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security:
  keyFile: <path-to-keyfile>
sharding:
  clusterRole: configsvr
replication:
  replSetName: <setname>
storage:
   dbpath: <path>

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.

Start the mongod specifying the --config option and the path to the configuration file.

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mongod --config <path-to-config>

Command Line

If using the command line parameters, for a config server replica set, start the mongod with the -keyFile, --configsvr, and --replSet parameters.

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mongod --keyFile <path-to-keyfile> --configsvr --replSet <setname> --dbpath <path>

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 more information on command line options, see the mongod reference page.

Make sure to use the original replica set name when restarting each member. You cannot change the name of a replica set.

8

Enforce Access Control for each Shard in the Sharded Cluster.

Running a mongod with the keyFile parameter enforces both Internal/Membership Authentication and Role-Based Access Control.

Start each mongod in the replica set using either a configuration file or the command line.

Configuration File

If using a configuration file, set the security.keyFile option to the keyfile’s path and the replication.replSetName option to the original name of the replica set.

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security:
  keyFile: <path-to-keyfile>
replication:
  replSetName: <setname>
storage:
   dbPath: <path>

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.

Start the mongod specifying the --config option and the path to the configuration file.

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mongod --config <path-to-config-file>

Command Line

If using the command line parameters, start the mongod and specify the --keyFile and --replSet parameters.

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mongod --keyfile <path-to-keyfile> --replSet <setname> --dbpath <path>

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 more information on startup parameters, see the mongod reference page.

Make sure to use the original replica set name when restarting each member. You cannot change the name of a replica set.

Repeat this step until all shards in the cluster are online.

9

Create a Shard-Local User Administrator (Optional).

Important

The Localhost Exception allows clients connected over the localhost interface to create users on a mongod enforcing access control. After creating the first user, the Localhost Exception closes.

The first user must have privileges to create other users, such as a user with the userAdminAnyDatabase. This ensures that you can create additional users after the Localhost Exception closes.

If at least one user does not have privileges to create users, once the localhost exception closes you may be unable to create or modify users with new privileges, and therefore unable to access certain functions or operations.

For each shard replica set in the cluster, connect a mongo shell to the primary member over the localhost interface. You must run the mongo on the same machine as the target mongod to use the localhost interface.

Create a user with the userAdminAnyDatabase role on the admin database. This user can create additional users for the shard replica set as necessary. Creating this user also closes the Localhost Exception.

The following example creates the shard-local user fred on the admin database.

Important

Passwords should be random, long, and complex to ensure system security and to prevent or delay malicious access.

Tip

Starting in version 4.2 of the mongo shell, you can use the passwordPrompt() method in conjunction with various user authentication/management methods/commands to prompt for the password instead of specifying the password directly in the method/command call. However, you can still specify the password directly as you would with earlier versions of the mongo shell.

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admin = db.getSiblingDB("admin")
admin.createUser(
  {
    user: "fred",
    pwd: passwordPrompt(),  // or cleartext password
    roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]
  }
)

10

Enforce Access Control for the mongos servers.

Running a mongod with the keyFile parameter enforces both Internal/Membership Authentication and Role-Based Access Control.

Start each mongos in the replica set using either a configuration file or the command line.

Configuration File

If using a configuration file, set the security.keyFile to the keyfile`s path and the sharding.configDB to the replica set name and at least one member of the replica set in <replSetName>/<host:port> format.

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security:
  keyFile: <path-to-keyfile>
sharding:
  configDB: <configReplSetName>/cfg1.example.net:27019,cfg2.example.net:27019,...

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.

Start the mongos specifying the --config option and the path to the configuration file.

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mongos --config <path-to-config-file>

Command Line

If using command line parameters start the mongos and specify the --keyFile and --configdb parameters.

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mongos --keyFile <path-to-keyfile> --configdb <configReplSetName>/cfg1.example.net:27019,cfg2.example.net:27019,...

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.

At this point, the entire sharded cluster is back online and can communicate internally using the keyfile specified. However, external programs like the mongo shell need to use a correctly provisioned user in order to read or write to the cluster.

11

Connect to the mongos instance over the localhost interface.

Connect a mongo shell to one of the mongos instances over the localhost interface. You must run the mongo shell on the same physical machine as the mongos instance.

The localhost interface is only available since no users have been created for the deployment. The localhost interface closes after the creation of the first user.

12

Create the user administrator.

Important

After you create the first user, the localhost exception is no longer available.

The first user must have privileges to create other users, such as a user with the userAdminAnyDatabase. This ensures that you can create additional users after the Localhost Exception closes.

If at least one user does not have privileges to create users, once the localhost exception closes you cannot create or modify users, and therefore may be unable to perform necessary operations.

Add a user using the db.createUser() method. The user should have at minimum the userAdminAnyDatabase role on the admin database.

Important

Passwords should be random, long, and complex to ensure system security and to prevent or delay malicious access.

The following example creates the user fred on the admin database:

Tip

Starting in version 4.2 of the mongo shell, you can use the passwordPrompt() method in conjunction with various user authentication/management methods/commands to prompt for the password instead of specifying the password directly in the method/command call. However, you can still specify the password directly as you would with earlier versions of the mongo shell.

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admin = db.getSiblingDB("admin")
admin.createUser(
  {
    user: "fred",
    pwd:  passwordPrompt(),     // or cleartext password
    roles: [ { role: "userAdminAnyDatabase", db: "admin" } ]
  }
)

See Database User Roles for a full list of built-in roles and related to database administration operations.

13

Authenticate as the user administrator.

Use db.auth() to authenticate as the user administrator to create additional users:

Tip

Starting in version 4.2 of the mongo shell, you can use the passwordPrompt() method in conjunction with various user authentication/management methods/commands to prompt for the password instead of specifying the password directly in the method/command call. However, you can still specify the password directly as you would with earlier versions of the mongo shell.

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db.getSiblingDB("admin").auth("fred", passwordPrompt()) // or cleartext password

Enter the password when prompted.

Alternatively, connect a new mongo shell to the target replica set member using the -u <username>, -p <password>, and the --authenticationDatabase "admin" parameters. You must use the Localhost Exception to connect to the mongos.

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mongo -u "fred" -p  --authenticationDatabase "admin"

If you do not specify the password to the -p command-line option, the mongo shell prompts for the password.

14

Create Administrative User for Cluster Management

The cluster administrator user has the clusterAdmin role for the sharded cluster and not the shard-local cluster administrator.

The following example creates the user ravi on the admin database.

Important

Passwords should be random, long, and complex to ensure system security and to prevent or delay malicious access.

Tip

Starting in version 4.2 of the mongo shell, you can use the passwordPrompt() method in conjunction with various user authentication/management methods/commands to prompt for the password instead of specifying the password directly in the method/command call. However, you can still specify the password directly as you would with earlier versions of the mongo shell.

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db.getSiblingDB("admin").createUser(
  {
    "user" : "ravi",
    "pwd" : passwordPrompt(),     // or cleartext password
    roles: [ { "role" : "clusterAdmin", "db" : "admin" } ]
  }
)

See Cluster Administration Roles for a full list of built-in roles related to replica set and sharded cluster operations.

15

Authenticate as cluster admin.

To perform sharding operations, authenticate as a clusterAdmin user with either the db.auth() method or a new mongo shell with the username, password, and authenticationDatabase parameters.

Note

This is the cluster administrator for the sharded cluster and not the shard-local cluster administrator.

16

Start the balancer.

Start the balancer.

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sh.startBalancer()

Starting in MongoDB 4.2, sh.startBalancer() also enables auto-splitting for the sharded cluster.

Use the sh.getBalancerState() to verify the balancer has started.

See Manage Sharded Cluster Balancer for tutorials on the sharded cluster balancer.

17

Create additional users (Optional).

Create users to allow clients to connect and access the sharded cluster. See Database User Roles for available built-in roles, such as read and readWrite. You may also want additional administrative users. For more information on users, see Users.

To create additional users, you must authenticate as a user with userAdminAnyDatabase or userAdmin roles.

x.509 Internal Authentication

For details on using x.509 for internal authentication, see Use x.509 Certificate for Membership Authentication.

To upgrade from keyfile internal authentication to x.509 internal authentication, see Upgrade from Keyfile Authentication to x.509 Authentication.

See also

Sharded Cluster Components

Operational Restrictions in Sharded Clusters

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