Apache Kudu Security

This document applies to Apache Kudu version 1.17.0. Please consult the documentation of the appropriate release that’s applicable to the version of the Kudu cluster.

Kudu includes security features which allow Kudu clusters to be hardened against access from unauthorized users. This guide describes the security features provided by Kudu. Configuring a Secure Kudu Cluster lists essential configuration options when deploying a secure Kudu cluster. Known Limitations contains a list of known deficiencies in Kudu’s security capabilities.


Kudu can be configured to enforce secure authentication among servers, and between clients and servers. Authentication prevents untrusted actors from gaining access to Kudu, and securely identifies the connecting user or services for authorization checks. Authentication in Kudu is designed to interoperate with other secure Hadoop components by utilizing Kerberos.

Authentication can be configured on Kudu servers using the --rpc_authentication flag, which can be set to required, optional, or disabled. By default, the flag is set to optional. When required, Kudu will reject connections from clients and servers who lack authentication credentials. When optional, Kudu will attempt to use strong authentication. When disabled or strong authentication fails for 'optional', by default Kudu will only allow unauthenticated connections from trusted subnets, which are private networks (,,,, and local subnets of all local network interfaces. Unauthenticated connections from publicly routable IPs will be rejected.

The trusted subnets can be configured using the --trusted_subnets flag, which can be set to IP blocks in CIDR notation separated by comma. Set it to '' to allow unauthenticated connections from all remote IP addresses. However, if network access is not otherwise restricted by a firewall, malicious users may be able to gain unauthorized access. This can be mitigated if authentication is configured to be required.

When the --rpc_authentication flag is set to optional, the cluster does not prevent access from unauthenticated users. To secure a cluster, use --rpc_authentication=required.

Internal PKI

Kudu uses an internal PKI system to issue X.509 certificates to servers in the cluster. Connections between peers who have both obtained certificates will use TLS for authentication, which doesn’t require contacting the Kerberos KDC. These certificates are only used for internal communication among Kudu servers, and between Kudu clients and servers. The certificates are never presented in a public facing protocol.

By using internally-issued certificates, Kudu offers strong authentication which scales to huge clusters, and allows TLS encryption to be used without requiring you to manually deploy certificates on every node.

Authentication Tokens

After authenticating to a secure cluster, the Kudu client will automatically request an authentication token from the Kudu master. An authentication token encapsulates the identity of the authenticated user and carries the master’s RSA signature so that its authenticity can be verified.

This token will be used to authenticate subsequent connections. By default, authentication tokens are only valid for seven days, so that even if a token were compromised, it could not be used indefinitely. For the most part, authentication tokens should be completely transparent to users. By using authentication tokens, Kudu takes advantage of strong authentication without paying the scalability cost of communicating with a central authority for every connection.

When used with distributed compute frameworks such as Spark, authentication tokens can simplify configuration and improve security. For example, the Kudu Spark connector will automatically retrieve an authentication token during the planning stage, and distribute the token to tasks. This allows Spark to work against a secured Kudu cluster where only the planner node has Kerberos credentials.

Client Authentication to Secure Kudu Clusters

Users running client Kudu applications must first run the kinit command to obtain a Kerberos ticket-granting ticket. For example:

$ kinit admin@EXAMPLE-REALM.COM

Once authenticated, you use the same client code to read from and write to Kudu servers with and without Kerberos configuration.


Kudu authentication is designed to scale to thousands of nodes, which requires avoiding unnecessary coordination with a central authentication authority (such as the Kerberos KDC). Instead, Kudu servers and clients will use Kerberos to establish initial trust with the Kudu master, and then use alternate credentials for subsequent connections. In particular, the master will issue internal X.509 certificates to servers, and temporary authentication tokens to clients.

Coarse-Grained Authorization

Kudu supports coarse-grained authorization of client requests based on the authenticated client Kerberos principal (i.e. user or service). The two levels of access which can be configured are:

  • Superuser - principals authorized as a superuser are able to perform certain administrative functionality such as using the kudu command line tool to diagnose or repair cluster issues.

  • User - principals authorized as a user are able to access and modify all data in the Kudu cluster. This includes the ability to create, drop, and alter tables as well as read, insert, update, and delete data.

Internally, Kudu has a third access level for the daemons themselves. This ensures that users cannot connect to the cluster and pose as tablet servers.

Access levels are granted using whitelist-style Access Control Lists (ACLs), one for each of the two levels. Each access control list either specifies a comma-separated list of users, or may be set to * to indicate that all authenticated users are able to gain access at the specified level. See Configuring a Secure Kudu Cluster below for examples.

The default value for the User ACL is *, which allows all users access to the cluster. However, if authentication is enabled, this still restricts access to only those users who are able to successfully authenticate via Kerberos. Unauthenticated users on the same network as the Kudu servers will be unable to access the cluster.

Fine-Grained Authorization

As of Kudu 1.12.0, Kudu can be configured to enforce fine-grained authorization across servers. This ensures that users can see only the data they are explicitly authorized to see. Kudu supports this by leveraging policies defined in Apache Ranger 2.1 and later.

Fine-grained authorization policies are not enforced when accessing the web UI. User data may appear on various pages of the web UI (e.g. in logs, metrics, scans, etc.). As such, it is recommended to either limit access to the web UI ports, or redact or disable the web UI entirely, as desired. See the instructions for securing the web UI for more details.

Apache Ranger

Apache Ranger models tabular objects stored in a Kudu cluster in the following hierarchy:

Ranger allows you to add separate service repositories to manage privileges for different Kudu clusters. Depending on the value of the ranger.plugin.kudu.service.name configuration in Ranger client, Kudu knows which service repository to connect to. For more details about Ranger service repository, see the Apache Ranger documentation.
  • Database - Kudu does not have the concept of a database. Therefore, a database is indicated as a prefix of table names with the format <database>.<table>. Since Kudu’s only restriction on table names is that they be valid UTF-8 encoded strings, Kudu considers special characters to be valid parts of database or table names. For example, if a managed Kudu table created from Impala (see Kudu Impala integration documentation) is named impala::bar.foo, its database will be impala::bar.

  • Table - a single Kudu table.

  • Column - a column within a Kudu table.

In Ranger, privileges are also associated with specific actions. Access to Kudu tables may rely on privileges on the following actions:




  • DROP




There are two additional access types:

  • ALL


If a user has the ALL privilege on a resource, they implicitly have privileges to perform any action on that resource (except those that require users to be a delegated admin, see below). Also, if a user is granted any privilege, they are able to perform actions requiring METADATA (e.g. opening the table) without having to explicitly grant METADATA privilege to them.

Finally, Ranger supports a delegate admin flag which is independent of the action types (it’s not implied by ALL and doesn’t imply METADATA). This is similar to the GRANT OPTION part of ALL WITH GRANT OPTION in SQL as it is required to modify privileges in Ranger and change the owner of a Kudu table.

A user with the delegate admin privilege on a resource can grant any privilege to themselves and others.

While the action types are hierarchical, in terms of privilege evaluation, Ranger doesn’t have the concept of hierarchy. For instance, if a user has SELECT privilege on a database, it does not imply that the user has SELECT privileges on every table belonging to that database. On the other hand, Ranger supports privilege wildcard matching. For example, db=a→table=* matches all the tables that belong to database a. Therefore, in Ranger users actually need the SELECT privilege granted on db=a→table=*→column=* to allow SELECT on every table and every column in database a.

Nevertheless, with Ranger integration, when a Kudu master receives a request, it consults Ranger to determine what privileges a user has. And the required policies documented in the policy section are enforced to determine whether the user is authorized to perform the requested action or not.

Even though Kudu table names remain case sensitive with Ranger integration, policy authorization is considered case-insensitive.

In addition to granting privileges to a user by username, privileges can also be granted to table owners using the special {OWNER} username. These policies are evaluated only when a user tries to perform an action on a table that they own. For example, a policy can be defined for the {OWNER} user and db=→table= resource, and it will automatically be applied when any table is accessed by its owner. This way administrators don’t need to choose between creating policies one by one for each table, and granting access to a wide range of users.

If a user has ALL and delegate admin privileges on a table only via ownership and no privileges by username, they can effectively lock themselves out by giving away ownership.

Authorization Tokens

Rather than having every tablet server communicate directly with the underlying authorization service (Ranger), privileges are propagated and checked via authorization tokens. These tokens encapsulate what privileges a user has on a given table. Tokens are generated by the master and returned to Kudu clients upon opening a Kudu table. Kudu clients automatically attach authorization tokens when sending requests to tablet servers.

Authorization tokens are a means to limiting the number of nodes directly accessing the authorization service to retrieve privileges. As such, since the expected number of tablet servers in a cluster is much higher than the number of Kudu masters, they are only used to authorize requests sent to tablet servers. Kudu masters fetch privileges directly from the authorization service or cache. See Ranger Client Caching for more details of Kudu’s privilege cache.

Similar to the validity interval for authentication tokens, to limit the window of potential unwanted access if a token becomes compromised, authorization tokens are valid for five minutes by default. The acquisition and renewal of a token is hidden from the user, as Kudu clients automatically retrieve new tokens when existing tokens expire.

When a tablet server that has been configured to enforce fine-grained access control receives a request, it checks the privileges in the attached token, rejecting it if the privileges are not sufficient to perform the requested operation, or if it is invalid (e.g. expired).

Trusted Users

It may be desirable to allow certain users to view and modify any data stored in Kudu. Such users can be specified via the --trusted_user_acl master configuration. Trusted users can perform any operation that would otherwise require fine-grained privileges, without Kudu consulting the authorization service.

Additionally, some services that interact with Kudu may authorize requests on behalf of their end users. For example, Apache Impala authorizes queries on behalf of its users, and sends requests to Kudu as the Impala service user, commonly "impala". Since Impala authorizes requests on its own, to avoid extraneous communication between the authorization service and Kudu, the Impala service user should be listed as a trusted user.

When accessing Kudu through Impala, Impala enforces its own fine-grained authorization policy. This policy is similar to Kudu’s and can be found in Impala’s authorization documentation.

Configuring the Integration with Apache Ranger

Ranger is often configured with Kerberos authentication. See Configuring a Secure Kudu Cluster for how to configure Kudu to authenticate via Kerberos.
  • After building Kudu from source, find the kudu-subprocess.jar under the build directory (e.g. build/release/bin). Note its path, as it is the one to the JAR file containing the Ranger subprocess, which houses the Ranger client that Kudu will use to communicate with the Ranger server.

  • Use the kudu table list tool to find any table names in the cluster that are not Ranger-compatible, which are names that begin or end with a period. Also check that there are no two table names that only differ by case, since authorization is case-insensitive. For those tables that don’t comply with the requirements, use the kudu table rename_table tool to rename the tables.

  • Create Ranger client ranger-kudu-security.xml configuration file, and note down the directory containing this file.

  <description>Directory where Ranger policies are cached after successful retrieval from the Ranger service</description>
  <description>Name of the Ranger service repository storing policies for this Kudu cluster</description>
  <description>Ranger Admin URL</description>
  <description>Ranger client implementation to retrieve policies from the Ranger service</description>
  <description>Path to the file containing SSL details to connect Ranger Admin</description>
  <description>Ranger client policy polling interval</description>
  • When Secure Socket Layer (SSL) is enabled for Ranger Admin, add ranger-kudu-policymgr-ssl.xml file to the Ranger client configuration directory with the following configurations:

  <description>Java keystore files</description>
  <description>Java keystore credential file</description>
  <description>Java truststore file</description>
  <description>Java truststore credential file</description>
  • Set the following configurations on the Kudu master:

# The path to directory containing Ranger client configuration. This example
# assumes the path is '/kudu/ranger-config'.

# The path where the Java binary was installed. This example assumes
# '$JAVA_HOME=/usr/local'

# The path to the JAR file containing the Ranger subprocess. This example
# assumes '$KUDU_HOME=/kudu'

# This example ACL setup allows the 'impala' user to access all data stored in
# Kudu, assuming Impala will authorize requests on its own. The 'kudu' user is
# also granted access to all Kudu data, which may facilitate testing and
# debugging (such as running the 'kudu cluster ksck' tool).
  • Set the following configurations on the tablet servers:

  • Add a Kudu service repository with the following configurations via the Ranger Admin web UI:

# This example setup configures the Kudu service user as a privileged user to be
# able to retrieve authorization policies stored in Ranger.


Ranger Client Caching

On the other hand, privilege cache in Kudu master is disabled with Ranger integration, since Ranger provides client side cache the use privileges and can periodically poll the privilege store for any changes. When a change is detected, the cache will be automatically updated.

Update the ranger.plugin.kudu.policy.pollIntervalMs property specified in ranger-kudu-security.xml to set how often the Ranger client cache refreshes the privileges from the Ranger service.

Policy for Kudu Masters

The following authorization policy is enforced by Kudu masters.

Table 1. Authorization Policy for Masters
Operation Required Privilege



CreateTable with an owner different than the logged in user

ALL ON DATABASE and delegate admin



AlterTable (with no rename)


AlterTable (with rename)

ALL ON TABLE <old-table> and CREATE ON DATABASE <new-database>

AlterTable (with owner change)

ALL ON TABLE and delegate admin













Policy for Kudu Tablet Servers

The following authorization policy is enforced by Kudu tablet servers.

Table 2. Authorization Policy for Tablet Servers
Operation Required Privilege



METADATA ON TABLE and SELECT ON COLUMN for each projected column and each predicate column

Scan (no projected columns, equivalent to COUNT(*))


SELECT ON COLUMN for each column in the table

Scan (with virtual columns)


SELECT ON COLUMN for each column in the table

Scan (in ORDERED mode)

<privileges required for a Scan> and SELECT ON COLUMN for each primary key column










SELECT ON COLUMN for each primary key column and SELECT ON COLUMN for each projected column


User must be configured in --superuser_acl


User must be configured in --superuser_acl

Unlike Impala, Kudu only supports all-or-nothing access to a table’s schema, rather than showing only authorized columns.


Kudu allows all communications among servers and between clients and servers to be encrypted with TLS, and the data to be encrypted at rest with AES.

Data in Transit

Encryption in transit can be configured on Kudu servers using the --rpc_encryption flag, which can be set to required, optional, or disabled. By default, the flag is set to optional. When required, Kudu will reject unencrypted connections. When optional, Kudu will attempt to use encryption. Same as authentication, when disabled or encryption fails for optional, Kudu will only allow unencrypted connections from trusted subnets and reject any unencrypted connections from publicly routable IPs. To secure a cluster, use --rpc_encryption=required.

Kudu will automatically turn off encryption on local loopback connections, since traffic from these connections is never exposed externally. This allows locality-aware compute frameworks like Spark and Impala to avoid encryption overhead, while still ensuring data confidentiality.

Data at Rest

It’s also possible to encrypt data at rest. Kudu supports AES-128-CTR, AES-192-CTR, and AES-256-CTR ciphers to encrypt data. Each physical file is encrypted with a unique key (File Key), which in turn is encrypted with the server’s own key (Server Key), which is encrypted by the Cluster Key stored in a third-party Key Management Service (KMS). Kudu supports Apache Ranger KMS and Apache Hadoop KMS (they are API-compatible).

Encryption at rest can be enabled with the --encrypt_data_at_rest=true flag. As the default key provider is NOT secure (it stores the Server Keys in cleartext and a Cluster Key is not used), the key provider should be set to ranger-kms using the encryption_key_provider flag and its URL set with ranger_kms_url. Before starting the server, a key must exist in the key provider with the same name as passed to Kudu with the --encryption_cluster_key_name flag.

When data is encrypted, CLI tools accessing the file system directly need to be provided with the same flags and the instance file from a data, WAL, or metadata directory must also be set with the --instance_file flag, for example:

$ kudu wal dump --encrypt_data_at_rest=true --encryption_key_provider=ranger-kms \
  --ranger_kms_url=https://ranger-kms.example.com:9292/kms \
  --instance_file=/path/to/wal/instance \
Enabling data at rest encryption is supported only on fresh installations. When encryption is enabled and there are pre-existing Kudu directories, Kudu will fail to start. Disabling it on an existing cluster is also unsupported. Existing Kudu clusters can be migrated in-place by re-adding the existing servers as encrypted one by one, and waiting for the data to be fully replicated after each step to make sure there is no data loss.

Web UI Encryption

The Kudu web UI can be configured to use secure HTTPS encryption by providing each server with TLS certificates. See Configuring a Secure Kudu Cluster for more information on web UI HTTPS configuration.

Web UI Redaction

To prevent sensitive data from being exposed in the web UI, all row data is redacted. Table metadata, such as table names, column names, and partitioning information is not redacted. The web UI can be completely disabled by setting the --webserver_enabled=false flag on Kudu servers.

Disabling the web UI will also disable REST endpoints such as /metrics. Monitoring systems rely on these endpoints to gather metrics data.

Log Security

To prevent sensitive data from being included in Kudu server logs, all row data is redacted by default. By setting the --redact=log flag, redaction will be disabled in the web UI but retained for server logs. Alternatively, --redact=none can be used to disable redaction completely.

Configuring a Secure Kudu Cluster

The following configuration parameters should be set on all servers (master and tablet server) in order to ensure that a Kudu cluster is secure:

# Connection Security
# -------------------

# Web UI Security
# ---------------
# optional

# If you prefer to disable the web UI entirely:

# Coarse-grained authorization
# ----------------------------

# This example ACL setup allows the 'impala' user as well as the
# 'nightly_etl_service_account' principal access to all data in the
# Kudu cluster. The 'hadoopadmin' user is allowed to use administrative
# tooling. Note that, by granting access to 'impala', other users
# may access data in Kudu via the Impala service subject to its own
# authorization rules.

# Data at rest encryption
# -----------------------

# This example data at rest encryption setup enables data at rest encryption for
# Kudu using Ranger KMS as the Cluster Key provider. The
# encryption_cluster_key_name is the default one, and if a key is created with
# this name in Ranger KMS, it can be omitted.
--encryption_cluster_key_name=kudu_cluster_key # optional

See Configuring the Integration with Apache Ranger to see an example of how to enable fine-grained authorization via Apache Ranger.

Further information about these flags can be found in the configuration flag reference.

Known Limitations

Kudu has a few known security limitations:

External PKI

Kudu does not support externally-issued certificates for internal wire encryption (server to server and client to server).

On-disk Encryption

Kudu does not have built-in on-disk encryption. However, Kudu can be used with whole-disk encryption tools such as dm-crypt.