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Encryption and Authentication with SSL

SSL Overview

With SSL authentication, the server authenticates the client (also called “2-way authentication”). Since SSL authentication requires SSL encryption, this page shows you how to configure both at the same time. It is a superset of configurations required just for SSL encryption.

By default, Apache Kafka® communicates in PLAINTEXT, which means that all data is sent in the clear. To encrypt communication, it is recommended to configure all the Confluent Platform components in your deployment to use SSL encryption.

Quick note on terminology: Secure Sockets Layer (SSL) is the predecessor of Transport Layer Security (TLS), and SSL has been deprecated since June 2015. However, for historical reasons, Kafka (like Java) uses the term SSL instead of TLS in configuration and code, which can be a bit confusing. This document uses only the term SSL.

SSL can be configured for encryption or authentication. You may configure just SSL encryption (by default SSL encryption includes certificate authentication of the server) and independently choose a separate mechanism for client authentication, e.g. SSL, SASL, etc. Note that SSL encryption, technically speaking, already enables 1-way authentication in which the client authenticates the server certificate. So when referring to SSL authentication, it is really referring to 2-way authentication in which the broker also authenticates the client certificate.

Note that enabling SSL may have a performance impact due to encryption overhead.

SSL uses private-key/certificates pairs which are used during the SSL handshake process.

• each broker needs its own private-key/certificate pair, and the client uses the certificate to authenticate the broker
• each logical client needs a private-key/certificate pair if client authentication is enabled, and the broker uses the certificate to authenticate the client

Each broker and logical client can be configured with a truststore, which is used to determine which certificates (broker or logical client identities) to trust (authenticate). The truststore can be configured in many ways, consider the following two examples:

1. the truststore contains one or many certificates: the broker or logical client will trust any certificate listed in the truststore
2. the truststore contains a Certificate Authority (CA): the broker or logical client will trust any certificate that was signed by the CA in the truststore

Using the CA (2) is more convenient, because adding a new broker or client doesn’t require a change to the truststore. The CA case (2) is outlined in this diagram.

However, with the CA case (2), Kafka does not conveniently support blocking authentication for individual brokers or clients that were previously trusted via this mechanism (certificate revocation is typically done via Certificate Revocation Lists or the Online Certificate Status Protocol), so one would have to rely on authorization to block access. In contrast, with case (1), blocking authentication would be achieved by removing the broker or client’s certificate from the truststore.

Creating SSL Keys and Certificates

Refer to the Security Tutorial which describes how to create SSL keys and certificates.

Brokers

Configure all brokers in the Kafka cluster to accept secure connections from clients. Any configuration changes made to the broker will require a rolling restart.

Enable security for Kafka brokers as described in the section below. Additionally, if you are using Confluent Control Center or Auto Data Balancer, configure your brokers for:

• Confluent Metrics Reporter

1. Configure the truststore, keystore, and password in the server.properties file of every broker. Since this stores passwords directly in the broker configuration file, it is important to restrict access to these files via file system permissions.

   ssl.truststore.location=/var/private/ssl/kafka.server.truststore.jks
   ssl.truststore.password=test1234
   ssl.keystore.location=/var/private/ssl/kafka.server.keystore.jks
   ssl.keystore.password=test1234
   ssl.key.password=test1234
   

   Note: ssl.truststore.password is technically optional but highly recommended. If a password is not set, access to the truststore is still available, but integrity checking is disabled.

2. If you want to enable SSL for inter-broker communication, add the following to the broker properties file (it defaults to PLAINTEXT):

   security.inter.broker.protocol=SSL
   

3. Configure the ports for the Apache Kafka® brokers to listen for client and inter-broker SSL connections. We need to configure listeners, and optionally advertised.listeners if the value is different from listeners.

   listeners=SSL://kafka1:9093
   advertised.listeners=SSL://0.0.0.0:9093
   

4. Configure both SSL ports and PLAINTEXT ports if:

   • SSL is not enabled for inter-broker communication
   • Some clients connecting to the cluster do not use SSL

   listeners=PLAINTEXT://kafka1:9092,SSL://kafka1:9093
   advertised.listeners=PLAINTEXT://0.0.0.0:9092,SSL://0.0.0.0:9093
   

   Note that advertised.host.name and advertised.port configure a single PLAINTEXT port and are incompatible with secure protocols. Please use advertised.listeners instead.

5. To enable the broker to authenticate clients (2-way authentication), you need to configure all the brokers for client authentication. We recommend configuring this to required. (We discourage requested because misconfigured clients will still connect successfully and it provides a false sense of security)

   ssl.client.auth=required
   

   Note

   If any of the SASL authentication mechanisms are enabled for a given listener, then SSL client authentication is disabled even if ssl.client.auth=required is configured, and the broker will authenticate clients only via SASL on that listener.

Optional settings

ssl.endpoint.identification.algorithm The endpoint identification algorithm used by clients to validate server host name. The default value is HTTPS. Clients including client connections created by the broker for inter-broker communication verify that the broker host name matches the host name in the broker’s certificate. Server host name verification may be disabled by setting ssl.endpoint.identification.algorithm to an empty string.

• Type: string
• Default: none
• Importance: medium

ssl.cipher.suites

A cipher suite is a named combination of authentication, encryption, MAC and key exchange algorithm used to negotiate the security settings for a network connection using TLS or SSL network protocol

• Type: list
• Default: null (by default, all supported cipher suites are enabled)
• Importance: medium

ssl.enabled.protocols

The list of protocols enabled for SSL connections

• Type: list
• Default: TLSv1.2,TLSv1.1,TLSv1
• Importance: medium

ssl.truststore.type

The file format of the truststore file.

• Type: string
• Default: JKS
• Importance: medium

Due to import regulations in some countries, the Oracle implementation limits the strength of cryptographic algorithms available by default. If stronger algorithms are needed (for example, AES with 256-bit keys), the JCE Unlimited Strength Jurisdiction Policy Files must be obtained and installed in the JDK/JRE. See the JCA Providers Documentation for more information.

Clients

The new Producer and Consumer clients support security for Kafka versions 0.9.0 and higher.

If you are using the Kafka Streams API, you can read on how to configure equivalent SSL and SASL parameters.

We assume client authentication is required by the broker in the following configuration example that you can store in a client properties file client-ssl.properties. Since this stores passwords directly in the broker configuration file, it is important to restrict access to these files via file system permissions.

bootstrap.servers=kafka1:9093
security.protocol=SSL
ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
ssl.truststore.password=test1234
ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
ssl.keystore.password=test1234
ssl.key.password=test1234

Note: ssl.truststore.password is technically optional but highly recommended. If a password is not set, access to the truststore is still available, but integrity checking is disabled.

Examples using kafka-console-producer and kafka-console-consumer, passing in the client-ssl.properties file with the properties defined above:

bin/kafka-console-producer --broker-list kafka1:9093 --topic test --producer.config client-ssl.properties
bin/kafka-console-consumer --bootstrap-server kafka1:9093 --topic test --consumer.config client-ssl.properties --from-beginning

Optional settings

Here are some optional settings:

ssl.endpoint.identification.algorithm The endpoint identification algorithm used by clients to validate server host name. The default value is HTTPS. Clients verify that the broker host name matches the host name in the broker’s certificate. Server host name verification may be disabled by setting ssl.endpoint.identification.algorithm to an empty string.

• Type: string
• Default: none
• Importance: medium

ssl.provider The name of the security provider used for SSL connections. Default value is the default security provider of the JVM.

• Type: string
• Default: null
• Importance: medium

ssl.cipher.suites A cipher suite is a named combination of authentication, encryption, MAC and key exchange algorithm used to negotiate the security settings for a network connection using TLS or SSL network protocol

• Type: list
• Default: null (by default, all supported cipher suites are enabled)
• Importance: medium

ssl.enabled.protocols The list of protocols enabled for SSL connections

• Type: list
• Default: TLSv1.2,TLSv1.1,TLSv1
• Importance: medium

ssl.truststore.type The file format of the truststore file.

• Type: string
• Default: JKS
• Importance: medium

ZooKeeper

The version of ZooKeeper that is bundled with Kafka does not support SSL.

Kafka Connect

This section describes how to enable security for Kafka Connect. Securing Kafka Connect requires that you configure security for:

1. Kafka Connect workers: part of the Kafka Connect API, a worker is really just an advanced client, underneath the covers
2. Kafka Connect connectors: connectors may have embedded producers or consumers, so you must override the default configurations for Connect producers used with source connectors and Connect consumers used with sink connectors
3. Kafka Connect REST: Kafka Connect exposes a REST API that can be configured to use SSL using additional properties

Configure security for Kafka Connect as described in the section below. Additionally, if you are using Confluent Control Center streams monitoring for Kafka Connect, configure security for:

• Confluent Monitoring Interceptors
• Confluent Metrics Reporter

Configure the top-level settings in the Connect workers to use SSL by adding these properties in connect-distributed.properties. These top-level settings are used by the Connect worker for group coordination and to read and write to the internal topics which are used to track the cluster’s state (e.g. configs and offsets). Here we assume client authentication is required by the brokers.

bootstrap.servers=kafka1:9093
security.protocol=SSL
ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
ssl.truststore.password=test1234
ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
ssl.keystore.password=test1234
ssl.key.password=test1234

Connect workers manage the producers used by source connectors and the consumers used by sink connectors. So, for the connectors to leverage security, you also have to override the default producer/consumer configuration that the worker uses. Here we assume client authentication is required by the brokers. Depending on whether the connector is a source or sink connector:

• For source connectors: configure the same properties adding the producer prefix.

  producer.bootstrap.servers=kafka1:9093
  producer.security.protocol=SSL
  producer.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
  producer.ssl.truststore.password=test1234
  producer.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
  producer.ssl.keystore.password=test1234
  producer.ssl.key.password=test1234
  

• For sink connectors: configure the same properties adding the consumer prefix.

  consumer.bootstrap.servers=kafka1:9093
  consumer.security.protocol=SSL
  consumer.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
  consumer.ssl.truststore.password=test1234
  consumer.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
  consumer.ssl.keystore.password=test1234
  consumer.ssl.key.password=test1234
  

Confluent Replicator

Confluent Replicator is a type of Kafka source connector that replicates data from a source to destination Kafka cluster. An embedded consumer inside Replicator consumes data from the source cluster, and an embedded producer inside the Kafka Connect worker produces data to the destination cluster.

Replicator version 4.0 and earlier requires a connection to ZooKeeper in the origin and destination Kafka clusters. If ZooKeeper is configured for authentication, the client configures the ZooKeeper security credentials via the global JAAS configuration setting -Djava.security.auth.login.config on the Connect workers, and the ZooKeeper security credentials in the origin and destination clusters must be the same.

To configure Confluent Replicator security, you must configure the Replicator connector as shown below and additionally you must configure:

• Kafka Connect

To add SSL to the Confluent Replicator embedded consumer, modify the Replicator JSON properties file

Here is an example subset of configuration properties to add for SSL encryption and authentication. Here we assume client authentication is required by the brokers.

{
  "name":"replicator",
    "config":{
      ....
      "src.kafka.bootstrap.servers" : "kafka1:9093",
      "src.kafka.security.protocol" : "SSL",
      "src.kafka.ssl.truststore.location" : "/var/private/ssl/kafka.client.truststore.jks",
      "src.kafka.ssl.truststore.password" : "test1234",
      "src.kafka.ssl.keystore.location" : "/var/private/ssl/kafka.client.keystore.jks",
      "src.kafka.ssl.keystore.password" : "test1234",
      "src.kafka.ssl.key.password" : "test1234",
      ....
    }
  }
}

Confluent Control Center

Confluent Control Center uses Kafka Streams as a state store, so if all the Kafka brokers in the cluster backing Control Center are secured, then the Control Center application also needs to be secured.

Enable security for the Control Center application as described in the section below. Additionally, configure security for the following components:

• Confluent Metrics Reporter: required on the production cluster being monitored
• Confluent Monitoring Interceptors: optional if you are using Control Center streams monitoring

Enable SSL for Control Center in the etc/confluent-control-center/control-center.properties file. Here we assume client authentication is required by the brokers.

confluent.controlcenter.streams.security.protocol=SSL
confluent.controlcenter.streams.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
confluent.controlcenter.streams.ssl.truststore.password=test1234
confluent.controlcenter.streams.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
confluent.controlcenter.streams.ssl.keystore.password=test1234
confluent.controlcenter.streams.ssl.key.password=test1234

Confluent Metrics Reporter

This section describes how to enable SSL encryption and authentication for Confluent Metrics Reporter, which is used for Confluent Control Center and Auto Data Balancer.

To add SSL for the Confluent Metrics Reporter, add the following to the server.properties file on the brokers in the Kafka cluster being monitored. Here we assume client authentication is required by the brokers.

confluent.metrics.reporter.bootstrap.servers=kafka1:9093
confluent.metrics.reporter.security.protocol=SSL
confluent.metrics.reporter.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
confluent.metrics.reporter.ssl.truststore.password=test1234
confluent.metrics.reporter.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
confluent.metrics.reporter.ssl.keystore.password=test1234
confluent.metrics.reporter.ssl.key.password=test1234

Confluent Monitoring Interceptors

Confluent Monitoring Interceptors are used for Confluent Control Center streams monitoring. This section describes how to enable security for Confluent Monitoring Interceptors in three places:

1. General clients
2. Kafka Connect
3. Confluent Replicator

Interceptors for General Clients

For Confluent Control Center stream monitoring to work with Kafka clients, you must configure SSL encryption and authentication for the Confluent Monitoring Interceptors in each client.

1. Verify that the client has configured interceptors.

• Producer:

  interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor
  

• Consumer:

  interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor
  

Configure SSL encryption and authentication for the interceptor. Here we assume client authentication is required by the brokers.

confluent.monitoring.interceptor.bootstrap.servers=kafka1:9093
confluent.monitoring.interceptor.security.protocol=SSL
confluent.monitoring.interceptor.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
confluent.monitoring.interceptor.ssl.truststore.password=test1234
confluent.monitoring.interceptor.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
confluent.monitoring.interceptor.ssl.keystore.password=test1234
confluent.monitoring.interceptor.ssl.key.password=test1234

Interceptors for Kafka Connect

For Confluent Control Center stream monitoring to work with Kafka Connect, you need to configure SSL for the Confluent Monitoring Interceptors in Kafka Connect. Here we assume client authentication is required by the brokers. Configure the Connect workers by adding these properties in connect-distributed.properties, depending on whether the connectors are sources or sinks.

• Source connector: configure the Confluent Monitoring Interceptors for SSL encryption and authentication with the producer prefix.

  producer.interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringProducerInterceptor
  producer.confluent.monitoring.interceptor.bootstrap.servers=kafka1:9093
  producer.confluent.monitoring.interceptor.security.protocol=SSL
  producer.confluent.monitoring.interceptor.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
  producer.confluent.monitoring.interceptor.ssl.truststore.password=test1234
  producer.confluent.monitoring.interceptor.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
  producer.confluent.monitoring.interceptor.ssl.keystore.password=test1234
  producer.confluent.monitoring.interceptor.ssl.key.password=test1234
  

• Sink connector: configure the Confluent Monitoring Interceptors for SSL encryption and authentication with the consumer prefix.

  consumer.interceptor.classes=io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor
  consumer.confluent.monitoring.interceptor.bootstrap.servers=kafka1:9093
  consumer.confluent.monitoring.interceptor.security.protocol=SSL
  consumer.confluent.monitoring.interceptor.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
  consumer.confluent.monitoring.interceptor.ssl.truststore.password=test1234
  consumer.confluent.monitoring.interceptor.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
  consumer.confluent.monitoring.interceptor.ssl.keystore.password=test1234
  consumer.confluent.monitoring.interceptor.ssl.key.password=test1234
  

Interceptors for Replicator

For Confluent Control Center stream monitoring to work with Replicator, you must configure SSL for the Confluent Monitoring Interceptors in the Replicator JSON configuration file. Here is an example subset of configuration properties to add for SSL encryption and authentication.

{
  "name":"replicator",
    "config":{
      ....
      "src.consumer.group.id": "replicator",
      "src.consumer.interceptor.classes": "io.confluent.monitoring.clients.interceptor.MonitoringConsumerInterceptor",
      "src.consumer.confluent.monitoring.interceptor.security.protocol": "SSL",
      "src.consumer.confluent.monitoring.interceptor.bootstrap.servers": "kafka1:9093",
      "src.consumer.confluent.monitoring.interceptor.ssl.truststore.location": "/var/private/ssl/kafka.client.truststore.jks",
      "src.consumer.confluent.monitoring.interceptor.ssl.truststore.password": "test1234",
      "src.consumer.confluent.monitoring.interceptor.ssl.keystore.location": "/var/private/ssl/kafka.client.keystore.jks",
      "src.consumer.confluent.monitoring.interceptor.ssl.keystore.password": "test1234",
      "src.consumer.confluent.monitoring.interceptor.ssl.key.password": "test1234",
      ....
    }
  }
}

Schema Registry

Schema Registry uses Kafka to persist schemas, and so it acts as a client to write data to the Kafka cluster. Therefore, if the Kafka brokers are configured for security, you should also configure Schema Registry to use security. You may also refer to the complete list of Schema Registry configuration options.

The following is an example subset of schema-registry.properties configuration parameters to add for SSL encryption and authentication. Here we assume client authentication is required by the brokers.

kafkastore.bootstrap.servers=SSL://kafka1:9093
kafkastore.security.protocol=SSL
kafkastore.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
kafkastore.ssl.truststore.password=test1234
kafkastore.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
kafkastore.ssl.keystore.password=test1234
kafkastore.ssl.key.password=test1234

REST Proxy

Securing Confluent REST Proxy with SSL encryption and authentication requires that you configure security between:

1. REST clients and the REST Proxy (HTTPS)
2. REST proxy and the Kafka cluster

You may also refer to the complete list of REST Proxy configuration options.

First configure HTTPS between REST clients and the REST Proxy. The following is an example subset of kafka-rest.properties configuration parameters to configure HTTPS.

ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
ssl.truststore.password=test1234
ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
ssl.keystore.password=test1234
ssl.key.password=test1234

Then, configure SSL encryption and authentication between REST proxy and the Kafka cluster. The following is an example subset of kafka-rest.properties configuration parameters to add for SSL encryption and authentication. Here we assume client authentication is required by the brokers.

client.bootstrap.servers=kafka1:9093
client.security.protocol=SSL
client.ssl.truststore.location=/var/private/ssl/kafka.client.truststore.jks
client.ssl.truststore.password=test1234
client.ssl.keystore.location=/var/private/ssl/kafka.client.keystore.jks
client.ssl.keystore.password=test1234
client.ssl.key.password=test1234

SSL Logging

Enable SSL debug logging at the JVM level by starting the Kafka broker and/or clients with the javax.net.debug system property. For example:

export KAFKA_OPTS=-Djavax.net.debug=all
bin/kafka-server-start etc/kafka/server.properties

Tip

These instructions assume you are installing Confluent Platform by using ZIP or TAR archives. For more information, see On-Premises Deployments.

Once you start the broker you should be able to see in the server.log:

with addresses: PLAINTEXT -> EndPoint(192.168.64.1,9092,PLAINTEXT),SSL -> EndPoint(192.168.64.1,9093,SSL)

To verify if the server’s keystore and truststore are setup correctly you can run the following command:

openssl s_client -debug -connect localhost:9093 -tls1

Note: TLSv1 should be listed under ssl.enabled.protocols.

In the output of this command you should see the server’s certificate:

-----BEGIN CERTIFICATE-----
{variable sized random bytes}
-----END CERTIFICATE-----
subject=/C=US/ST=CA/L=Santa Clara/O=org/OU=org/CN=Joe Smith
issuer=/C=US/ST=CA/L=Santa Clara/O=org/OU=org/CN=kafka/emailAddress=test@test.com

You can find more details on this in the Oracle documentation on debugging SSL/TLS connections.

If the certificate does not show up with the openssl command, or if there are any other error messages, then your keys or certificates are not setup correctly. Review your configurations.