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Chapter 11. Managing TLS certificates

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AMQ Streams supports encrypted communication between the Kafka and AMQ Streams components using the TLS protocol. Communication between Kafka brokers (interbroker communication), between ZooKeeper nodes (internodal communication), and between those components and the AMQ Streams operators is always encrypted. Communication between Kafka clients and Kafka brokers is encrypted according to how the cluster is configured. For the Kafka and AMQ Streams components, TLS certificates are also used for authentication.

The Cluster Operator automatically sets up and renews TLS certificates to enable encryption and authentication within your cluster. It also sets up other TLS certificates if you want to enable encryption or TLS authentication between Kafka brokers and clients. Certificates provided by users are not renewed.

You can provide your own server certificates, called Kafka listener certificates, for TLS listeners or external listeners which have TLS encryption enabled. For more information, see Section 11.7, “Kafka listener certificates”.

Figure 11.1. Example architecture of the communication secured by TLS

Secure Communication

11.1. Certificate Authorities

To support encryption, each AMQ Streams component needs its own private keys and public key certificates. All component certificates are signed by an internal Certificate Authority (CA) called the cluster CA.

Similarly, each Kafka client application connecting to AMQ Streams using TLS client authentication needs to provide private keys and certificates. A second internal CA, named the clients CA, is used to sign certificates for the Kafka clients.

11.1.1. CA certificates

Both the cluster CA and clients CA have a self-signed public key certificate.

Kafka brokers are configured to trust certificates signed by either the cluster CA or clients CA. Components that clients do not need to connect to, such as ZooKeeper, only trust certificates signed by the cluster CA. Unless TLS encryption for external listeners is disabled, client applications must trust certificates signed by the cluster CA. This is also true for client applications that perform mutual TLS authentication.

By default, AMQ Streams automatically generates and renews CA certificates issued by the cluster CA or clients CA. You can configure the management of these CA certificates in the Kafka.spec.clusterCa and Kafka.spec.clientsCa objects. Certificates provided by users are not renewed.

You can provide your own CA certificates for the cluster CA or clients CA. For more information, see Section 11.1.2, “Installing your own CA certificates”. If you provide your own certificates, you must manually renew them when needed.

11.1.2. Installing your own CA certificates

This procedure describes how to install your own CA certificates and keys instead of using the CA certificates and private keys generated by the Cluster Operator.

You can use this procedure to install your own cluster or client CA certificates.

The procedure describes renewal of CA certificates in PEM format. You can also use certificates in PKCS #12 format.

Prerequisites

  • The Cluster Operator is running.
  • A Kafka cluster is not yet deployed.

  • Your own X.509 certificates and keys in PEM format for the cluster CA or clients CA.

    • If you want to use a cluster or clients CA which is not a Root CA, you have to include the whole chain in the certificate file. The chain should be in the following order:

      1. The cluster or clients CA
      2. One or more intermediate CAs
      3. The root CA
    • All CAs in the chain should be configured as a CA in the X509v3 Basic Constraints.

Procedure

  1. Put your CA certificate in the corresponding Secret.

    1. Delete the existing secret: 

      oc delete secret CA-CERTIFICATE-SECRET

      CA-CERTIFICATE-SECRET is the name of the Secret, which is CLUSTER-NAME-cluster-ca-cert for the cluster CA certificate and CLUSTER-NAME-clients-ca-cert for the clients CA certificate.

      Ignore any "Not Exists" errors.

    2. Create and label the new secret 

      oc create secret generic CA-CERTIFICATE-SECRET --from-file=ca.crt=CA-CERTIFICATE-FILENAME

  2. Put your CA key in the corresponding Secret.

    1. Delete the existing secret: 

      oc delete secret CA-KEY-SECRET

      CA-KEY-SECRET is the name of CA key, which is CLUSTER-NAME-cluster-ca for the cluster CA key and CLUSTER-NAME-clients-ca for the clients CA key.

    2. Create the new secret: 

      oc create secret generic CA-KEY-SECRET --from-file=ca.key=CA-KEY-SECRET-FILENAME

  3. Label the secrets with the labels strimzi.io/kind=Kafka and strimzi.io/cluster=CLUSTER-NAME: 

    oc label secret CA-CERTIFICATE-SECRET strimzi.io/kind=Kafka strimzi.io/cluster=CLUSTER-NAME
oc label secret CA-KEY-SECRET strimzi.io/kind=Kafka strimzi.io/cluster=CLUSTER-NAME

  4. Create the Kafka resource for your cluster, configuring either the Kafka.spec.clusterCa or the Kafka.spec.clientsCa object to not use generated CAs:

    Example fragment Kafka resource configuring the cluster CA to use certificates you supply for yourself

    kind: Kafka
version: kafka.strimzi.io/v1beta2
spec:
  # ...
  clusterCa:
    generateCertificateAuthority: false

Additional resources

11.2. Secrets

AMQ Streams uses Secrets to store private keys and certificates for Kafka cluster components and clients. Secrets are used for establishing TLS encrypted connections between Kafka brokers, and between brokers and clients. They are also used for mutual TLS authentication.

  • A Cluster Secret contains a cluster CA certificate to sign Kafka broker certificates, and is used by a connecting client to establish a TLS encrypted connection with the Kafka cluster to validate broker identity.
  • A Client Secret contains a client CA certificate for a user to sign its own client certificate to allow mutual authentication against the Kafka cluster. The broker validates the client identity through the client CA certificate itself.
  • A User Secret contains a private key and certificate, which are generated and signed by the client CA certificate when a new user is created. The key and certificate are used for authentication and authorization when accessing the cluster.

Secrets provide private keys and certificates in PEM and PKCS #12 formats. Using private keys and certificates in PEM format means that users have to get them from the Secrets, and generate a corresponding truststore (or keystore) to use in their Java applications. PKCS #12 storage provides a truststore (or keystore) that can be used directly.

All keys are 2048 bits in size.

11.2.1. PKCS #12 storage

PKCS #12 defines an archive file format (.p12) for storing cryptography objects into a single file with password protection. You can use PKCS #12 to manage certificates and keys in one place.

Each Secret contains fields specific to PKCS #12.

  • The .p12 field contains the certificates and keys.
  • The .password field is the password that protects the archive.

11.2.2. Cluster CA Secrets

The following tables describe the Cluster Secrets that are managed by the Cluster Operator in a Kafka cluster.

Only the <cluster>-cluster-ca-cert Secret needs to be used by clients. All other Secrets described only need to be accessed by the AMQ Streams components. You can enforce this using OpenShift role-based access controls, if necessary.

Table 11.1. Fields in the <cluster>-cluster-ca Secret
FieldDescription

ca.key

The current private key for the cluster CA.

Table 11.2. Fields in the <cluster>-cluster-ca-cert Secret
FieldDescription

ca.p12

PKCS #12 archive file for storing certificates and keys.

ca.password

Password for protecting the PKCS #12 archive file.

ca.crt

The current certificate for the cluster CA.

Note

The CA certificates in <cluster>-cluster-ca-cert must be trusted by Kafka client applications so that they validate the Kafka broker certificates when connecting to Kafka brokers over TLS.

Table 11.3. Fields in the <cluster>-kafka-brokers Secret
FieldDescription

<cluster>-kafka-<num>.p12

PKCS #12 archive file for storing certificates and keys.

<cluster>-kafka-<num>.password

Password for protecting the PKCS #12 archive file.

<cluster>-kafka-<num>.crt

Certificate for Kafka broker pod <num>. Signed by a current or former cluster CA private key in <cluster>-cluster-ca.

<cluster>-kafka-<num>.key

Private key for Kafka broker pod <num>.

Table 11.4. Fields in the <cluster>-zookeeper-nodes Secret
FieldDescription

<cluster>-zookeeper-<num>.p12

PKCS #12 archive file for storing certificates and keys.

<cluster>-zookeeper-<num>.password

Password for protecting the PKCS #12 archive file.

<cluster>-zookeeper-<num>.crt

Certificate for ZooKeeper node <num>. Signed by a current or former cluster CA private key in <cluster>-cluster-ca.

<cluster>-zookeeper-<num>.key

Private key for ZooKeeper pod <num>.

Table 11.5. Fields in the <cluster>-entity-operator-certs Secret
FieldDescription

entity-operator_.p12

PKCS #12 archive file for storing certificates and keys.

entity-operator_.password

Password for protecting the PKCS #12 archive file.

entity-operator_.crt

Certificate for TLS communication between the Entity Operator and Kafka or ZooKeeper. Signed by a current or former cluster CA private key in <cluster>-cluster-ca.

entity-operator.key

Private key for TLS communication between the Entity Operator and Kafka or ZooKeeper.

11.2.3. Client CA Secrets

Table 11.6. Clients CA Secrets managed by the Cluster Operator in <cluster>
Secret nameField within SecretDescription

<cluster>-clients-ca

ca.key

The current private key for the clients CA.

<cluster>-clients-ca-cert

ca.p12

PKCS #12 archive file for storing certificates and keys.

ca.password

Password for protecting the PKCS #12 archive file.

ca.crt

The current certificate for the clients CA.

The certificates in <cluster>-clients-ca-cert are those which the Kafka brokers trust.

Note

<cluster>-clients-ca is used to sign certificates of client applications. It needs to be accessible to the AMQ Streams components and for administrative access if you are intending to issue application certificates without using the User Operator. You can enforce this using OpenShift role-based access controls if necessary.

11.2.4. Adding labels and annotations to Secrets

By configuring the clusterCaCert template property in the Kafka custom resource, you can add custom labels and annotations to the Cluster CA Secrets created by the Cluster Operator. Labels and annotations are useful for identifying objects and adding contextual information. You configure template properties in AMQ Streams custom resources.

Example template customization to add labels and annotations to Secrets

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
metadata:
  name: my-cluster
spec:
  kafka:
    # ...
    template:
      clusterCaCert:
        metadata:
          labels:
            label1: value1
            label2: value2
          annotations:
            annotation1: value1
            annotation2: value2
    # ...

For more information on configuring template properties, see Section 2.6, “Customizing OpenShift resources”.

11.2.5. Disabling ownerReference in the CA Secrets

By default, the Cluster and Client CA Secrets are created with an ownerReference property that is set to the Kafka custom resource. This means that, when the Kafka custom resource is deleted, the CA secrets are also deleted (garbage collected) by OpenShift.

If you want to reuse the CA for a new cluster, you can disable the ownerReference by setting the generateSecretOwnerReference property for the Cluster and Client CA Secrets to false in the Kafka configuration. When the ownerReference is disabled, CA Secrets are not deleted by OpenShift when the corresponding Kafka custom resource is deleted.

Example Kafka configuration with disabled ownerReference for Cluster and Client CAs

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
# ...
spec:
# ...
  clusterCa:
    generateSecretOwnerReference: false
  clientsCa:
    generateSecretOwnerReference: false
# ...

Additional resources

11.2.6. User Secrets

Table 11.7. Secrets managed by the User Operator
Secret nameField within SecretDescription

<user>

user.p12

PKCS #12 archive file for storing certificates and keys.

user.password

Password for protecting the PKCS #12 archive file.

user.crt

Certificate for the user, signed by the clients CA

user.key

Private key for the user

11.3. Certificate renewal and validity periods

Cluster CA and clients CA certificates are only valid for a limited time period, known as the validity period. This is usually defined as a number of days since the certificate was generated.

For CA certificates automatically created by the Cluster Operator, you can configure the validity period of:

  • Cluster CA certificates in Kafka.spec.clusterCa.validityDays
  • Client CA certificates in Kafka.spec.clientsCa.validityDays

The default validity period for both certificates is 365 days. Manually-installed CA certificates should have their own validity periods defined.

When a CA certificate expires, components and clients that still trust that certificate will not accept TLS connections from peers whose certificates were signed by the CA private key. The components and clients need to trust the new CA certificate instead.

To allow the renewal of CA certificates without a loss of service, the Cluster Operator will initiate certificate renewal before the old CA certificates expire.

You can configure the renewal period of the certificates created by the Cluster Operator:

  • Cluster CA certificates in Kafka.spec.clusterCa.renewalDays
  • Client CA certificates in Kafka.spec.clientsCa.renewalDays

The default renewal period for both certificates is 30 days.

The renewal period is measured backwards, from the expiry date of the current certificate.

Validity period against renewal period

Not Before                                     Not After
    |                                              |
    |<--------------- validityDays --------------->|
                              <--- renewalDays --->|

To make a change to the validity and renewal periods after creating the Kafka cluster, you configure and apply the Kafka custom resource, and manually renew the CA certificates. If you do not manually renew the certificates, the new periods will be used the next time the certificate is renewed automatically.

Example Kafka configuration for certificate validity and renewal periods

apiVersion: kafka.strimzi.io/v1beta2
kind: Kafka
# ...
spec:
# ...
  clusterCa:
    renewalDays: 30
    validityDays: 365
    generateCertificateAuthority: true
  clientsCa:
    renewalDays: 30
    validityDays: 365
    generateCertificateAuthority: true
# ...

The behavior of the Cluster Operator during the renewal period depends on the settings for the certificate generation properties, generateCertificateAuthority and generateCertificateAuthority.

true
If the properties are set to true, a CA certificate is generated automatically by the Cluster Operator, and renewed automatically within the renewal period.
false
If the properties are set to false, a CA certificate is not generated by the Cluster Operator. Use this option if you are installing your own certificates.

11.3.1. Renewal process with automatically generated CA certificates

The Cluster Operator performs the following process to renew CA certificates:

  1. Generate a new CA certificate, but retain the existing key. The new certificate replaces the old one with the name ca.crt within the corresponding Secret.
  2. Generate new client certificates (for ZooKeeper nodes, Kafka brokers, and the Entity Operator). This is not strictly necessary because the signing key has not changed, but it keeps the validity period of the client certificate in sync with the CA certificate.
  3. Restart ZooKeeper nodes so that they will trust the new CA certificate and use the new client certificates.
  4. Restart Kafka brokers so that they will trust the new CA certificate and use the new client certificates.
  5. Restart the Topic and User Operators so that they will trust the new CA certificate and use the new client certificates.

11.3.2. Client certificate renewal

The Cluster Operator is not aware of the client applications using the Kafka cluster.

When connecting to the cluster, and to ensure they operate correctly, client applications must:

  • Trust the cluster CA certificate published in the <cluster>-cluster-ca-cert Secret.

  • Use the credentials published in their <user-name> Secret to connect to the cluster.

    The User Secret provides credentials in PEM and PKCS #12 format, or it can provide a password when using SCRAM-SHA authentication. The User Operator creates the user credentials when a user is created.

You must ensure clients continue to work after certificate renewal. The renewal process depends on how the clients are configured.

If you are provisioning client certificates and keys manually, you must generate new client certificates and ensure the new certificates are used by clients within the renewal period. Failure to do this by the end of the renewal period could result in client applications being unable to connect to the cluster.

Note

For workloads running inside the same OpenShift cluster and namespace, Secrets can be mounted as a volume so the client Pods construct their keystores and truststores from the current state of the Secrets. For more details on this procedure, see Configuring internal clients to trust the cluster CA.

11.3.3. Manually renewing the CA certificates generated by the Cluster Operator

Cluster and clients CA certificates generated by the Cluster Operator auto-renew at the start of their respective certificate renewal periods. However, you can use the strimzi.io/force-renew annotation to manually renew one or both of these certificates before the certificate renewal period starts. You might do this for security reasons, or if you have changed the renewal or validity periods for the certificates.

A renewed certificate uses the same private key as the old certificate.

Note

If you are using your own CA certificates, the force-renew annotation cannot be used. Instead, follow the procedure for renewing your own CA certificates.

Prerequisites

  • The Cluster Operator is running.
  • A Kafka cluster in which CA certificates and private keys are installed.

Procedure

  1. Apply the strimzi.io/force-renew annotation to the Secret that contains the CA certificate that you want to renew.

    Table 11.8. Annotation for the Secret that forces renewal of certificates
    CertificateSecretAnnotate command

    Cluster CA

    KAFKA-CLUSTER-NAME-cluster-ca-cert

    oc annotate secret KAFKA-CLUSTER-NAME-cluster-ca-cert strimzi.io/force-renew=true

    Clients CA

    KAFKA-CLUSTER-NAME-clients-ca-cert

    oc annotate secret KAFKA-CLUSTER-NAME-clients-ca-cert strimzi.io/force-renew=true

    At the next reconciliation the Cluster Operator will generate a new CA certificate for the Secret that you annotated. If maintenance time windows are configured, the Cluster Operator will generate the new CA certificate at the first reconciliation within the next maintenance time window.

    Client applications must reload the cluster and clients CA certificates that were renewed by the Cluster Operator.

  2. Check the period the CA certificate is valid:

    For example, using an openssl command: 

    oc get secret CA-CERTIFICATE-SECRET -o 'jsonpath={.data.CA-CERTIFICATE}' | base64 -d | openssl x509 -subject -issuer -startdate -enddate -noout

    CA-CERTIFICATE-SECRET is the name of the Secret, which is KAFKA-CLUSTER-NAME-cluster-ca-cert for the cluster CA certificate and KAFKA-CLUSTER-NAME-clients-ca-cert for the clients CA certificate.

    CA-CERTIFICATE is the name of the CA certificate, such as jsonpath={.data.ca\.crt}.

    The command returns a notBefore and notAfter date, which is the validity period for the CA certificate.

    For example, for a cluster CA certificate: 

    subject=O = io.strimzi, CN = cluster-ca v0
issuer=O = io.strimzi, CN = cluster-ca v0
notBefore=Jun 30 09:43:54 2020 GMT
notAfter=Jun 30 09:43:54 2021 GMT

  3. Delete old certificates from the Secret.

    When components are using the new certificates, older certificates might still be active. Delete the old certificates to remove any potential security risk.

Additional resources

11.3.4. Replacing private keys used by the CA certificates generated by the Cluster Operator

You can replace the private keys used by the cluster CA and clients CA certificates generated by the Cluster Operator. When a private key is replaced, the Cluster Operator generates a new CA certificate for the new private key.

Note

If you are using your own CA certificates, the force-replace annotation cannot be used. Instead, follow the procedure for renewing your own CA certificates.

Prerequisites

  • The Cluster Operator is running.
  • A Kafka cluster in which CA certificates and private keys are installed.

Procedure

  • Apply the strimzi.io/force-replace annotation to the Secret that contains the private key that you want to renew.

    Table 11.9. Commands for replacing private keys
    Private key forSecretAnnotate command

    Cluster CA

    CLUSTER-NAME-cluster-ca

    oc annotate secret CLUSTER-NAME-cluster-ca strimzi.io/force-replace=true

    Clients CA

    CLUSTER-NAME-clients-ca

    oc annotate secret CLUSTER-NAME-clients-ca strimzi.io/force-replace=true

At the next reconciliation the Cluster Operator will:

  • Generate a new private key for the Secret that you annotated
  • Generate a new CA certificate

If maintenance time windows are configured, the Cluster Operator will generate the new private key and CA certificate at the first reconciliation within the next maintenance time window.

Client applications must reload the cluster and clients CA certificates that were renewed by the Cluster Operator.

Additional resources

11.3.5. Renewing your own CA certificates

This procedure describes how to renew CA certificates and keys you installed yourself, instead of using the certificates generated by the Cluster Operator.

If you are using your own certificates, the Cluster Operator will not renew them automatically. Therefore, it is important that you follow this procedure during the renewal period of the certificate in order to replace CA certificates that will soon expire.

The procedure describes the renewal of CA certificates in PEM format. You can also use certificates in PKCS #12 format.

Prerequisites

These could be generated using an openssl command, such as: 

openssl req -x509 -new -days NUMBER-OF-DAYS-VALID --nodes -out ca.crt -keyout ca.key

Procedure

  1. Check the details of the current CA certificates in the Secret: 

    oc describe secret CA-CERTIFICATE-SECRET

    CA-CERTIFICATE-SECRET is the name of the Secret, which is KAFKA-CLUSTER-NAME-cluster-ca-cert for the cluster CA certificate and KAFKA-CLUSTER-NAME-clients-ca-cert for the clients CA certificate.

  2. Create a directory to contain the existing CA certificates in the secret. 

    mkdir new-ca-cert-secret
cd new-ca-cert-secret

  3. Fetch the secret for each CA certificate you wish to renew: 

    oc get secret CA-CERTIFICATE-SECRET -o 'jsonpath={.data.CA-CERTIFICATE}' | base64 -d > CA-CERTIFICATE

    Replace CA-CERTIFICATE with the name of each CA certificate.

  4. Rename the old ca.crt file as ca-DATE.crt, where DATE is the certificate expiry date in the format YEAR-MONTH-DAYTHOUR-MINUTE-SECONDZ.

    For example ca-2018-09-27T17-32-00Z.crt. 

    mv ca.crt ca-$(date -u -d$(openssl x509 -enddate -noout -in ca.crt | sed 's/.*=//') +'%Y-%m-%dT%H-%M-%SZ').crt

  5. Copy your new CA certificate into the directory, naming it ca.crt: 

    cp PATH-TO-NEW-CERTIFICATE ca.crt

  6. Put your CA certificate in the corresponding Secret.

    1. Delete the existing secret: 

      oc delete secret CA-CERTIFICATE-SECRET

      CA-CERTIFICATE-SECRET is the name of the Secret, as returned in the first step.

      Ignore any "Not Exists" errors.

    2. Recreate the secret: 

      oc create secret generic CA-CERTIFICATE-SECRET --from-file=.

  7. Delete the directory you created: 

    cd ..
rm -r new-ca-cert-secret

  8. Put your CA key in the corresponding Secret.

    1. Delete the existing secret: 

      oc delete secret CA-KEY-SECRET

      CA-KEY-SECRET is the name of CA key, which is KAFKA-CLUSTER-NAME-cluster-ca for the cluster CA key and KAFKA-CLUSTER-NAME-clients-ca for the clients CA key.

    2. Recreate the secret with the new CA key: 

      oc create secret generic CA-KEY-SECRET --from-file=ca.key=CA-KEY-SECRET-FILENAME

  9. Label the secrets with the labels strimzi.io/kind=Kafka and strimzi.io/cluster=KAFKA-CLUSTER-NAME: 

    oc label secret CA-CERTIFICATE-SECRET strimzi.io/kind=Kafka strimzi.io/cluster=KAFKA-CLUSTER-NAME
oc label secret CA-KEY-SECRET strimzi.io/kind=Kafka strimzi.io/cluster=KAFKA-CLUSTER-NAME

11.4. TLS connections

11.4.1. ZooKeeper communication

Communication between the ZooKeeper nodes on all ports, as well as between clients and ZooKeeper, is encrypted using TLS.

Communication between Kafka brokers and ZooKeeper nodes is also encrypted.

11.4.2. Kafka inter-broker communication

Communication between Kafka brokers is always encrypted using TLS.

Unless the ControlPlaneListener feature gate is enabled, all inter-broker communication goes through an internal listener on port 9091. If you enable the feature gate, traffic from the control plane goes through an internal control plane listener on port 9090. Traffic from the data plane continues to use the existing internal listener on port 9091.

These internal listeners are not available to Kafka clients.

11.4.3. Topic and User Operators

All Operators use encryption for communication with both Kafka and ZooKeeper. In Topic and User Operators, a TLS sidecar is used when communicating with ZooKeeper.

11.4.4. Cruise Control

Cruise Control uses encryption for communication with both Kafka and ZooKeeper. A TLS sidecar is used when communicating with ZooKeeper.

11.4.5. Kafka Client connections

Encrypted or unencrypted communication between Kafka brokers and clients is configured using the tls property for spec.kafka.listeners.

11.5. Configuring internal clients to trust the cluster CA

This procedure describes how to configure a Kafka client that resides inside the OpenShift cluster — connecting to a TLS listener — to trust the cluster CA certificate.

The easiest way to achieve this for an internal client is to use a volume mount to access the Secrets containing the necessary certificates and keys.

Follow the steps to configure trust certificates that are signed by the cluster CA for Java-based Kafka Producer, Consumer, and Streams APIs.

Choose the steps to follow according to the certificate format of the cluster CA: PKCS #12 (.p12) or PEM (.crt).

The steps describe how to mount the Cluster Secret that verifies the identity of the Kafka cluster to the client pod.

Prerequisites

  • The Cluster Operator must be running.
  • There needs to be a Kafka resource within the OpenShift cluster.
  • You need a Kafka client application inside the OpenShift cluster that will connect using TLS, and needs to trust the cluster CA certificate.
  • The client application must be running in the same namespace as the Kafka resource.

Using PKCS #12 format (.p12)

  1. Mount the cluster Secret as a volume when defining the client pod.

    For example: 

    kind: Pod
apiVersion: v1
metadata:
  name: client-pod
spec:
  containers:
  - name: client-name
    image: client-name
    volumeMounts:
    - name: secret-volume
      mountPath: /data/p12
    env:
    - name: SECRET_PASSWORD
      valueFrom:
        secretKeyRef:
          name: my-secret
          key: my-password
  volumes:
  - name: secret-volume
    secret:
      secretName: my-cluster-cluster-ca-cert

    Here we’re mounting:

    • The PKCS #12 file into an exact path, which can be configured
    • The password into an environment variable, where it can be used for Java configuration

  2. Configure the Kafka client with the following properties:

    • A security protocol option:

      • security.protocol: SSL when using TLS for encryption (with or without TLS authentication).
      • security.protocol: SASL_SSL when using SCRAM-SHA authentication over TLS.
    • ssl.truststore.location with the truststore location where the certificates were imported.
    • ssl.truststore.password with the password for accessing the truststore.
    • ssl.truststore.type=PKCS12 to identify the truststore type.

Using PEM format (.crt)

  1. Mount the cluster Secret as a volume when defining the client pod.

    For example: 

    kind: Pod
apiVersion: v1
metadata:
  name: client-pod
spec:
  containers:
  - name: client-name
    image: client-name
    volumeMounts:
    - name: secret-volume
      mountPath: /data/crt
  volumes:
  - name: secret-volume
    secret:
      secretName: my-cluster-cluster-ca-cert
  2. Use the certificate with clients that use certificates in X.509 format.

11.6. Configuring external clients to trust the cluster CA

This procedure describes how to configure a Kafka client that resides outside the OpenShift cluster – connecting to an external listener – to trust the cluster CA certificate. Follow this procedure when setting up the client and during the renewal period, when the old clients CA certificate is replaced.

Follow the steps to configure trust certificates that are signed by the cluster CA for Java-based Kafka Producer, Consumer, and Streams APIs.

Choose the steps to follow according to the certificate format of the cluster CA: PKCS #12 (.p12) or PEM (.crt).

The steps describe how to obtain the certificate from the Cluster Secret that verifies the identity of the Kafka cluster.

Important

The <cluster-name>-cluster-ca-cert Secret will contain more than one CA certificate during the CA certificate renewal period. Clients must add all of them to their truststores.

Prerequisites

  • The Cluster Operator must be running.
  • There needs to be a Kafka resource within the OpenShift cluster.
  • You need a Kafka client application outside the OpenShift cluster that will connect using TLS, and needs to trust the cluster CA certificate.

Using PKCS #12 format (.p12)

  1. Extract the cluster CA certificate and password from the generated <cluster-name>-cluster-ca-cert Secret. 

    oc get secret <cluster-name>-cluster-ca-cert -o jsonpath='{.data.ca\.p12}' | base64 -d > ca.p12
    oc get secret <cluster-name>-cluster-ca-cert -o jsonpath='{.data.ca\.password}' | base64 -d > ca.password

  2. Configure the Kafka client with the following properties:

    • A security protocol option:

      • security.protocol: SSL when using TLS for encryption (with or without TLS authentication).
      • security.protocol: SASL_SSL when using SCRAM-SHA authentication over TLS.
    • ssl.truststore.location with the truststore location where the certificates were imported.
    • ssl.truststore.password with the password for accessing the truststore. This property can be omitted if it is not needed by the truststore.
    • ssl.truststore.type=PKCS12 to identify the truststore type.

Using PEM format (.crt)

  1. Extract the cluster CA certificate from the generated <cluster-name>-cluster-ca-cert Secret. 

    oc get secret <cluster-name>-cluster-ca-cert -o jsonpath='{.data.ca\.crt}' | base64 -d > ca.crt
  2. Use the certificate with clients that use certificates in X.509 format.

11.7. Kafka listener certificates

You can provide your own server certificates and private keys for the following types of listeners:

  • Internal TLS listeners for communication within the OpenShift cluster
  • External listeners (route, loadbalancer, ingress, and nodeport types), which have TLS encryption enabled, for communication between Kafka clients and Kafka brokers

These user-provided certificates are called Kafka listener certificates.

Providing Kafka listener certificates for external listeners allows you to leverage existing security infrastructure, such as your organization’s private CA or a public CA. Kafka clients will connect to Kafka brokers using Kafka listener certificates rather than certificates signed by the cluster CA or clients CA.

You must manually renew Kafka listener certificates when needed.

11.7.1. Providing your own Kafka listener certificates

This procedure shows how to configure a listener to use your own private key and server certificate, called a Kafka listener certificate.

Your client applications should use the CA public key as a trusted certificate in order to verify the identity of the Kafka broker.

Prerequisites

  • An OpenShift cluster.
  • The Cluster Operator is running.

  • For each listener, a compatible server certificate signed by an external CA.

Procedure

  1. Create a Secret containing your private key and server certificate: 

    oc create secret generic my-secret --from-file=my-listener-key.key --from-file=my-listener-certificate.crt

  2. Edit the Kafka resource for your cluster. Configure the listener to use your Secret, certificate file, and private key file in the configuration.brokerCertChainAndKey property.

    Example configuration for a loadbalancer external listener with TLS encryption enabled

    # ...
listeners:
  - name: plain
    port: 9092
    type: internal
    tls: false
  - name: external
    port: 9094
    type: loadbalancer
    tls: true
    authentication:
      type: tls
    configuration:
      brokerCertChainAndKey:
        secretName: my-secret
        certificate: my-listener-certificate.crt
        key: my-listener-key.key
# ...

    Example configuration for a TLS listener

    # ...
listeners:
  - name: plain
    port: 9092
    type: internal
    tls: false
  - name: tls
    port: 9093
    type: internal
    tls: true
    authentication:
      type: tls
    configuration:
      brokerCertChainAndKey:
        secretName: my-secret
        certificate: my-listener-certificate.crt
        key: my-listener-key.key
# ...

  3. Apply the new configuration to create or update the resource: 

    oc apply -f kafka.yaml

    The Cluster Operator starts a rolling update of the Kafka cluster, which updates the configuration of the listeners.

    Note

    A rolling update is also started if you update a Kafka listener certificate in a Secret that is already used by a TLS or external listener.

Additional resources

11.7.2. Alternative subjects in server certificates for Kafka listeners

In order to use TLS hostname verification with your own Kafka listener certificates, you must use the correct Subject Alternative Names (SANs) for each listener. The certificate SANs must specify hostnames for:

  • All of the Kafka brokers in your cluster
  • The Kafka cluster bootstrap service

You can use wildcard certificates if they are supported by your CA.

11.7.2.1. TLS listener SAN examples

Use the following examples to help you specify hostnames of the SANs in your certificates for TLS listeners.

Wildcards example

//Kafka brokers
*.<cluster-name>-kafka-brokers
*.<cluster-name>-kafka-brokers.<namespace>.svc

// Bootstrap service
<cluster-name>-kafka-bootstrap
<cluster-name>-kafka-bootstrap.<namespace>.svc

Non-wildcards example

// Kafka brokers
<cluster-name>-kafka-0.<cluster-name>-kafka-brokers
<cluster-name>-kafka-0.<cluster-name>-kafka-brokers.<namespace>.svc
<cluster-name>-kafka-1.<cluster-name>-kafka-brokers
<cluster-name>-kafka-1.<cluster-name>-kafka-brokers.<namespace>.svc
# ...

// Bootstrap service
<cluster-name>-kafka-bootstrap
<cluster-name>-kafka-bootstrap.<namespace>.svc

11.7.2.2. External listener SAN examples

For external listeners which have TLS encryption enabled, the hostnames you need to specify in certificates depends on the external listener type.

Table 11.10. SANs for each type of external listener
External listener typeIn the SANs, specify…​

Route

Addresses of all Kafka broker Routes and the address of the bootstrap Route.

You can use a matching wildcard name.

loadbalancer

Addresses of all Kafka broker loadbalancers and the bootstrap loadbalancer address.

You can use a matching wildcard name.

NodePort

Addresses of all OpenShift worker nodes that the Kafka broker pods might be scheduled to.

You can use a matching wildcard name.

Additional resources

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