In release 0.9.0.0, the Kafka community added a number of features that, used either separately or together, increases security in a Kafka cluster. These features are considered to be of beta quality. The following security measures are currently supported:
<li>Authentication of connections from brokers to ZooKeeper</li>
<li>Encryption of data transferred between brokers and clients, between brokers, or between brokers and tools using SSL (Note that there is a performance degradation when SSL is enabled, the magnitude of which depends on the CPU type and the JVM implementation.)</li>
<li>Authorization of read / write operations by clients</li>
<li>Authorization is pluggable and integration with external authorization services is supported</li>
It's worth noting that security is optional - non-secured clusters are supported, as well as a mix of authenticated, unauthenticated, encrypted and non-encrypted clients.
The first step of deploying HTTPS is to generate the key and the certificate for each machine in the cluster. You can use Java's keytool utility to accomplish this task.
You need to specify two parameters in the above command:
<ol>
<li>keystore: the keystore file that stores the certificate. The keystore file contains the private key of the certificate; therefore, it needs to be kept safely.</li>
<li>validity: the valid time of the certificate in days.</li>
</ol>
Ensure that common name (CN) matches exactly with the fully qualified domain name (FQDN) of the server. The client compares the CN with the DNS domain name to ensure that it is indeed connecting to the desired server, not the malicious one.</li>
After the first step, each machine in the cluster has a public-private key pair, and a certificate to identify the machine. The certificate, however, is unsigned, which means that an attacker can create such a certificate to pretend to be any machine.<p>
Therefore, it is important to prevent forged certificates by signing them for each machine in the cluster. A certificate authority (CA) is responsible for signing certificates. CA works likes a government that issues passports—the government stamps (signs) each passport so that the passport becomes difficult to forge. Other governments verify the stamps to ensure the passport is authentic. Similarly, the CA signs the certificates, and the cryptography guarantees that a signed certificate is computationally difficult to forge. Thus, as long as the CA is a genuine and trusted authority, the clients have high assurance that they are connecting to the authentic machines.
<b>Note:</b> If you configure the Kafka brokers to require client authentication by setting ssl.client.auth to be "requested" or "required" on the <ahref="#config_broker">Kafka brokers config</a> then you must provide a truststore for the Kafka brokers as well and it should have all the CA certificates that clients keys were signed by.
In contrast to the keystore in step 1 that stores each machine's own identity, the truststore of a client stores all the certificates that the client should trust. Importing a certificate into one's truststore also means trusting all certificates that are signed by that certificate. As the analogy above, trusting the government (CA) also means trusting all passports (certificates) that it has issued. This attribute is called the chain of trust, and it is particularly useful when deploying SSL on a large Kafka cluster. You can sign all certificates in the cluster with a single CA, and have all machines share the same truststore that trusts the CA. That way all machines can authenticate all other machines.</li>
The next step is to sign all certificates generated by step 1 with the CA generated in step 2. First, you need to export the certificate from the keystore:
The definitions of the parameters are the following:
<ol>
<li>keystore: the location of the keystore</li>
<li>ca-cert: the certificate of the CA</li>
<li>ca-key: the private key of the CA</li>
<li>ca-password: the passphrase of the CA</li>
<li>cert-file: the exported, unsigned certificate of the server</li>
<li>cert-signed: the signed certificate of the server</li>
</ol>
Here is an example of a bash script with all above steps. Note that one of the commands assumes a password of `test1234`, so either use that password or edit the command before running it.
<li>ssl.client.auth=none ("required" => client authentication is required, "requested" => client authentication is requested and client without certs can still connect. The usage of "requested" is discouraged as it provides a false sense of security and misconfigured clients will still connect successfully.)</li>
<li>ssl.cipher.suites (Optional). 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. (Default is an empty list)</li>
<li>ssl.enabled.protocols=TLSv1.2,TLSv1.1,TLSv1 (list out the SSL protocols that you are going to accept from clients. Do note that SSL is deprecated in favor of TLS and using SSL in production is not recommended)</li>
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 <ahref="http://www.oracle.com/technetwork/java/javase/downloads/index.html">JCE Unlimited Strength Jurisdiction Policy Files</a> must be obtained and installed in the JDK/JRE. See the
<ahref="https://docs.oracle.com/javase/8/docs/technotes/guides/security/SunProviders.html">JCA Providers Documentation</a> for more information.
SSL is supported only for the new Kafka Producer and Consumer, the older API is not supported. The configs for SSL will be the same for both producer and consumer.<br>
<li>ssl.provider (Optional). The name of the security provider used for SSL connections. Default value is the default security provider of the JVM.</li>
<li>ssl.cipher.suites (Optional). 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.</li>
If your organization is already using a Kerberos server (for example, by using Active Directory), there is no need to install a new server just for Kafka. Otherwise you will need to install one, your Linux vendor likely has packages for Kerberos and a short guide on how to install and configure it (<ahref="https://help.ubuntu.com/community/Kerberos">Ubuntu</a>, <ahref="https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Managing_Smart_Cards/installing-kerberos.html">Redhat</a>). Note that if you are using Oracle Java, you will need to download JCE policy files for your Java version and copy them to $JAVA_HOME/jre/lib/security.</li>
<li><b>Create Kerberos Principals</b><br>
If you are using the organization's Kerberos or Active Directory server, ask your Kerberos administrator for a principal for each Kafka broker in your cluster and for every operating system user that will access Kafka with Kerberos authentication (via clients and tools).</br>
If you have installed your own Kerberos, you will need to create these principals yourself using the following commands:
<li><b>Make sure all hosts can be reachable using hostnames</b> - it is a Kerberos requirement that all your hosts can be resolved with their FQDNs.</li>
<li>Add a suitably modified JAAS file similar to the one below to each Kafka broker's config directory, let's call it kafka_server_jaas.conf for this example (note that each broker should have its own keytab):
<tt>KafkaServer</tt> section in the JAAS file tells the broker which principal to use and the location of the keytab where this principal is stored. It
allows the broker to login using the keytab specified in this section. See <ahref="#security_sasl_brokernotes">notes</a> for more details on Zookeeper SASL configuration.
<li>Pass the JAAS and optionally the krb5 file locations as JVM parameters to each Kafka broker (see <ahref="https://docs.oracle.com/javase/8/docs/technotes/guides/security/jgss/tutorials/KerberosReq.html">here</a> for more details):
<li>Make sure the keytabs configured in the JAAS file are readable by the operating system user who is starting kafka broker.</li>
<li>Configure SASL port and SASL mechanisms in server.properties as described <ahref="#security_sasl_brokerconfig">here</a>.</pre> For example:
<pre> listeners=SASL_PLAINTEXT://host.name:port
security.inter.broker.protocol=SASL_PLAINTEXT
sasl.mechanism.inter.broker.protocol=GSSAPI
sasl.enabled.mechanisms=GSSAPI
</pre>
</li>We must also configure the service name in server.properties, which should match the principal name of the kafka brokers. In the above example, principal is "kafka/kafka1.hostname.com@EXAMPLE.com", so:
Clients (producers, consumers, connect workers, etc) will authenticate to the cluster with their own principal (usually with the same name as the user running the client), so obtain or create these principals as needed. Then create a JAAS file for each principal.
The KafkaClient section describes how the clients like producer and consumer can connect to the Kafka Broker. The following is an example configuration for a client using a keytab (recommended for long-running processes):
<li>Pass the JAAS and optionally krb5 file locations as JVM parameters to each client JVM (see <ahref="https://docs.oracle.com/javase/8/docs/technotes/guides/security/jgss/tutorials/KerberosReq.html">here</a> for more details):
<li><h4><aid="security_sasl_plain"href="#security_sasl_plain">Authentication using SASL/PLAIN</a></h4>
<p>SASL/PLAIN is a simple username/password authentication mechanism that is typically used with TLS for encryption to implement secure authentication.
Kafka supports a default implementation for SASL/PLAIN which can be extended for production use as described <ahref="#security_sasl_plain_production">here</a>.</p>
The username is used as the authenticated <code>Principal</code> for configuration of ACLs etc.
<li>Add a suitably modified JAAS file similar to the one below to each Kafka broker's config directory, let's call it kafka_server_jaas.conf for this example:
<li>SASL/PLAIN should be used only with SSL as transport layer to ensure that clear passwords are not transmitted on the wire without encryption.</li>
<li>The default implementation of SASL/PLAIN in Kafka specifies usernames and passwords in the JAAS configuration file as shown
<ahref="#security_sasl_plain_brokerconfig">here</a>. To avoid storing passwords on disk, you can plugin your own implementation of
<code>javax.security.auth.spi.LoginModule</code> that provides usernames and passwords from an external source. The login module implementation should
provide username as the public credential and password as the private credential of the <code>Subject</code>. The default implementation
<code>org.apache.kafka.common.security.plain.PlainLoginModule</code> can be used as an example.</li>
<li>In production systems, external authentication servers may implement password authentication. Kafka brokers can be integrated with these servers by adding
your own implementation of <code>javax.security.sasl.SaslServer</code>. The default implementation included in Kafka in the package
<code>org.apache.kafka.common.security.plain</code> can be used as an example to get started.
<ul>
<li>New providers must be installed and registered in the JVM. Providers can be installed by adding provider classes to
the normal <tt>CLASSPATH</tt> or bundled as a jar file and added to <tt><i>JAVA_HOME</i>/lib/ext</tt>.</li>
<li>Providers can be registered statically by adding a provider to the security properties file
<li>Follow the mechanism-specific steps in <ahref="#security_sasl_kerberos_brokerconfig">GSSAPI (Kerberos)</a>
and <ahref="#security_sasl_plain_brokerconfig">PLAIN</a> to configure SASL for the enabled mechanisms.</li>
</ol>
</li>
<li><h4><aid="saslmechanism_rolling_upgrade"href="#saslmechanism_rolling_upgrade">Modifying SASL mechanism in a Running Cluster</a></h4>
<p>SASL mechanism can be modified in a running cluster using the following sequence:</p>
<ol>
<li>Enable new SASL mechanism by adding the mechanism to <tt>sasl.enabled.mechanisms</tt> in server.properties for each broker. Update JAAS config file to include both
mechanisms as described <ahref="#security_sasl_multimechanism">here</a>. Incrementally bounce the cluster nodes.</li>
<li>Restart clients using the new mechanism.</li>
<li>To change the mechanism of inter-broker communication (if this is required), set <tt>sasl.mechanism.inter.broker.protocol</tt> in server.properties to the new mechanism and
incrementally bounce the cluster again.</li>
<li>To remove old mechanism (if this is required), remove the old mechanism from <tt>sasl.enabled.mechanisms</tt> in server.properties and remove the entries for the
old mechanism from JAAS config file. Incrementally bounce the cluster again.</li>
Kafka ships with a pluggable Authorizer and an out-of-box authorizer implementation that uses zookeeper to store all the acls. Kafka acls are defined in the general format of "Principal P is [Allowed/Denied] Operation O From Host H On Resource R". You can read more about the acl structure on KIP-11. In order to add, remove or list acls you can use the Kafka authorizer CLI. By default, if a Resource R has no associated acls, no one other than super users is allowed to access R. If you want to change that behavior, you can include the following in broker.properties.
By default, the SSL user name will be of the form "CN=writeuser,OU=Unknown,O=Unknown,L=Unknown,ST=Unknown,C=Unknown". One can change that by setting a customized PrincipalBuilder in broker.properties like the following.
By default, the SASL user name will be the primary part of the Kerberos principal. One can change that by setting <code>sasl.kerberos.principal.to.local.rules</code> to a customized rule in broker.properties.
The format of <code>sasl.kerberos.principal.to.local.rules</code> is a list where each rule works in the same way as the auth_to_local in <ahref="http://web.mit.edu/Kerberos/krb5-latest/doc/admin/conf_files/krb5_conf.html">Kerberos configuration file (krb5.conf)</a>. Each rules starts with RULE: and contains an expression in the format [n:string](regexp)s/pattern/replacement/g. See the kerberos documentation for more details. An example of adding a rule to properly translate user@MYDOMAIN.COM to user while also keeping the default rule in place is:
Kafka Authorization management CLI can be found under bin directory with all the other CLIs. The CLI script is called <b>kafka-acls.sh</b>. Following lists all the options that the script supports:
<p></p>
<tableclass="data-table">
<tr>
<th>Option</th>
<th>Description</th>
<th>Default</th>
<th>Option type</th>
</tr>
<tr>
<td>--add</td>
<td>Indicates to the script that user is trying to add an acl.</td>
<td></td>
<td>Action</td>
</tr>
<tr>
<td>--remove</td>
<td>Indicates to the script that user is trying to remove an acl.</td>
<td></td>
<td>Action</td>
</tr>
<tr>
<td>--list</td>
<td>Indicates to the script that user is trying to list acls.</td>
<td></td>
<td>Action</td>
</tr>
<tr>
<td>--authorizer</td>
<td>Fully qualified class name of the authorizer.</td>
<td>key=val pairs that will be passed to authorizer for initialization. For the default authorizer the example values are: zookeeper.connect=localhost:2181</td>
<td>Specifies the consumer-group as resource.</td>
<td></td>
<td>Resource</td>
</tr>
<tr>
<td>--allow-principal</td>
<td>Principal is in PrincipalType:name format that will be added to ACL with Allow permission. <br>You can specify multiple --allow-principal in a single command.</td>
<td></td>
<td>Principal</td>
</tr>
<tr>
<td>--deny-principal</td>
<td>Principal is in PrincipalType:name format that will be added to ACL with Deny permission. <br>You can specify multiple --deny-principal in a single command.</td>
Suppose you want to add an acl "Principals User:Bob and User:Alice are allowed to perform Operation Read and Write on Topic Test-Topic from IP 198.51.100.0 and IP 198.51.100.1". You can do that by executing the CLI with following options:
By default all principals that don't have an explicit acl that allows access for an operation to a resource are denied. In rare cases where an allow acl is defined that allows access to all but some principal we will have to use the --deny-principal and --deny-host option. For example, if we want to allow all users to Read from Test-topic but only deny User:BadBob from IP 198.51.100.3 we can do so using following commands:
Note that ``--allow-host`` and ``deny-host`` only support IP addresses (hostnames are not supported).
Above examples add acls to a topic by specifying --topic [topic-name] as the resource option. Similarly user can add acls to cluster by specifying --cluster and to a consumer group by specifying --group [group-name].</li>
Removing acls is pretty much the same. The only difference is instead of --add option users will have to specify --remove option. To remove the acls added by the first example above we can execute the CLI with following options:
We can list acls for any resource by specifying the --list option with the resource. To list all acls for Test-topic we can execute the CLI with following options:
<li><b>Adding or removing a principal as producer or consumer</b><br>
The most common use case for acl management are adding/removing a principal as producer or consumer so we added convenience options to handle these cases. In order to add User:Bob as a producer of Test-topic we can execute the following command:
<h3><aid="security_rolling_upgrade"href="#security_rolling_upgrade">7.5 Incorporating Security Features in a Running Cluster</a></h3>
You can secure a running cluster via one or more of the supported protocols discussed previously. This is done in phases:
<p></p>
<ul>
<li>Incrementally bounce the cluster nodes to open additional secured port(s).</li>
<li>Restart clients using the secured rather than PLAINTEXT port (assuming you are securing the client-broker connection).</li>
<li>Incrementally bounce the cluster again to enable broker-to-broker security (if this is required)</li>
<li>A final incremental bounce to close the PLAINTEXT port.</li>
</ul>
<p></p>
The specific steps for configuring SSL and SASL are described in sections <ahref="#security_ssl">7.2</a> and <ahref="#security_sasl">7.3</a>.
Follow these steps to enable security for your desired protocol(s).
<p></p>
The security implementation lets you configure different protocols for both broker-client and broker-broker communication.
These must be enabled in separate bounces. A PLAINTEXT port must be left open throughout so brokers and/or clients can continue to communicate.
<p></p>
When performing an incremental bounce stop the brokers cleanly via a SIGTERM. It's also good practice to wait for restarted replicas to return to the ISR list before moving onto the next node.
<p></p>
As an example, say we wish to encrypt both broker-client and broker-broker communication with SSL. In the first incremental bounce, a SSL port is opened on each node:
In the final bounce we secure the cluster by closing the PLAINTEXT port:
<pre>
listeners=SSL://broker1:9092
security.inter.broker.protocol=SSL</pre>
Alternatively we might choose to open multiple ports so that different protocols can be used for broker-broker and broker-client communication. Say we wished to use SSL encryption throughout (i.e. for broker-broker and broker-client communication) but we'd like to add SASL authentication to the broker-client connection also. We would achieve this by opening two additional ports during the first bounce:
The metadata stored in ZooKeeper is such that only brokers will be able to modify the corresponding znodes, but znodes are world readable. The rationale behind this decision is that the data stored in ZooKeeper is not sensitive, but inappropriate manipulation of znodes can cause cluster disruption. We also recommend limiting the access to ZooKeeper via network segmentation (only brokers and some admin tools need access to ZooKeeper if the new consumer and new producer are used).
If you are running a version of Kafka that does not support security or simply with security disabled, and you want to make the cluster secure, then you need to execute the following steps to enable ZooKeeper authentication with minimal disruption to your operations:
<li>Perform a rolling restart setting the JAAS login file, which enables brokers to authenticate. At the end of the rolling restart, brokers are able to manipulate znodes with strict ACLs, but they will not create znodes with those ACLs</li>
<li>Perform a second rolling restart of brokers, this time setting the configuration parameter <tt>zookeeper.set.acl</tt> to true, which enables the use of secure ACLs when creating znodes</li>
<li>Execute the ZkSecurityMigrator tool. To execute the tool, there is this script: <tt>./bin/zookeeper-security-migration.sh</tt> with <tt>zookeeper.acl</tt> set to secure. This tool traverses the corresponding sub-trees changing the ACLs of the znodes</li>
</ol>
<p>It is also possible to turn off authentication in a secure cluster. To do it, follow these steps:</p>
<ol>
<li>Perform a rolling restart of brokers setting the JAAS login file, which enables brokers to authenticate, but setting <tt>zookeeper.set.acl</tt> to false. At the end of the rolling restart, brokers stop creating znodes with secure ACLs, but are still able to authenticate and manipulate all znodes</li>
<li>Execute the ZkSecurityMigrator tool. To execute the tool, run this script <tt>./bin/zookeeper-security-migration.sh</tt> with <tt>zookeeper.acl</tt> set to unsecure. This tool traverses the corresponding sub-trees changing the ACLs of the znodes</li>
<li>Perform a second rolling restart of brokers, this time omitting the system property that sets the JAAS login file</li>
</ol>
Here is an example of how to run the migration tool:
It is also necessary to enable authentication on the ZooKeeper ensemble. To do it, we need to perform a rolling restart of the server and set a few properties. Please refer to the ZooKeeper documentation for more detail:
