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Kafka

What is Kafka

Kafka is a Kubernetes Custom Resource Definitions (CRD). It provides declarative configuration for Kafka in a Kubernetes native way. You only need to describe the desired database configuration in a Kafkaobject, and the KubeDB operator will create Kubernetes objects in the desired state for you.

Kafka Spec

As with all other Kubernetes objects, a Kafka needs apiVersion, kind, and metadata fields. It also needs a .spec section. Below is an example Kafka object.

apiVersion: kubedb.com/v1alpha2
kind: Kafka
metadata:
  name: kafka
  namespace: demo
spec:
  authSecret:
    name: kafka-admin-cred
  configSecret:
    name: kafka-custom-config
  enableSSL: true
  healthChecker:
    failureThreshold: 3
    periodSeconds: 20
    timeoutSeconds: 10
  keystoreCredSecret:
    name: kafka-keystore-cred
  podTemplate:
    metadata:
      annotations:
        passMe: ToDatabasePod
      labels:
        thisLabel: willGoToPod
    controller:
      annotations:
        passMe: ToPetSet
      labels:
        thisLabel: willGoToSts
  storageType: Durable
  deletionPolicy: DoNotTerminate
  tls:
    certificates:
      - alias: server
        secretName: kafka-server-cert
      - alias: client
        secretName: kafka-client-cert
    issuerRef:
      apiGroup: cert-manager.io
      kind: Issuer
      name: kafka-ca-issuer
  topology:
    broker:
      replicas: 3
      resources:
        limits:
          memory: 1Gi
        requests:
          cpu: 500m
          memory: 1Gi
      storage:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
      suffix: broker
    controller:
      replicas: 3
      resources:
        limits:
          memory: 1Gi
        requests:
          cpu: 500m
          memory: 1Gi
      storage:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 1Gi
        storageClassName: standard
      suffix: controller
  monitor:
    agent: prometheus.io/operator
    prometheus:
      exporter:
        port: 56790
      serviceMonitor:
        labels:
          release: prometheus
        interval: 10s
  version: 3.6.1

spec.version

spec.version is a required field specifying the name of the KafkaVersion crd where the docker images are specified. Currently, when you install KubeDB, it creates the following Kafka resources,

• 3.3.2
• 3.4.1
• 3.5.1
• 3.5.2
• 3.6.0
• 3.6.1

spec.replicas

spec.replicas the number of members in Kafka replicaset.

If spec.topology is set, then spec.replicas needs to be empty. Instead use spec.topology.controller.replicas and spec.topology.broker.replicas. You need to set both of them for topology clustering.

KubeDB uses PodDisruptionBudget to ensure that majority of these replicas are available during voluntary disruptions so that quorum is maintained.

spec.authSecret

spec.authSecret is an optional field that points to a Secret used to hold credentials for kafka admin user. If not set, KubeDB operator creates a new Secret {kafka-object-name}-auth for storing the password for admin user for each Kafka object.

We can use this field in 3 mode.

1. Using an external secret. In this case, You need to create an auth secret first with required fields, then specify the secret name when creating the Kafka object using spec.authSecret.name & set spec.authSecret.externallyManaged to true.

authSecret:
  name: <your-created-auth-secret-name>
  externallyManaged: true

2. Specifying the secret name only. In this case, You need to specify the secret name when creating the Kafka object using spec.authSecret.name. externallyManaged is by default false.

authSecret:
  name: <intended-auth-secret-name>

3. Let KubeDB do everything for you. In this case, no work for you.

AuthSecret contains a user key and a password key which contains the username and password respectively for Kafka admin user.

Example:

$ kubectl create secret generic kf-auth -n demo \
--from-literal=username=jhon-doe \
--from-literal=password=6q8u_2jMOW-OOZXk
secret "kf-auth" created

apiVersion: v1
data:
  password: NnE4dV8yak1PVy1PT1pYaw==
  username: amhvbi1kb2U=
kind: Secret
metadata:
  name: kf-auth
  namespace: demo
type: Opaque

Secrets provided by users are not managed by KubeDB, and therefore, won’t be modified or garbage collected by the KubeDB operator (version 0.13.0 and higher).

spec.configSecret

spec.configSecret is an optional field that points to a Secret used to hold custom Kafka configuration. If not set, KubeDB operator will use default configuration for Kafka.

spec.topology

spec.topology represents the topology configuration for Kafka cluster in KRaft mode.

When spec.topology is set, the following fields needs to be empty, otherwise validating webhook will throw error.

• spec.replicas
• spec.podTemplate
• spec.storage

spec.topology.broker

broker represents configuration for brokers of Kafka. In KRaft Topology mode clustering each pod can act as a single dedicated Kafka broker.

Available configurable fields:

• topology.broker:
  • replicas (: "1") - is an optional field to specify the number of nodes (ie. pods ) that act as the dedicated Kafka broker pods. Defaults to 1.
  • suffix (: "broker") - is an optional field that is added as the suffix of the broker PetSet name. Defaults to broker.
  • storage is a required field that specifies how much storage to claim for each of the broker pods.
  • resources (: "cpu: 500m, memory: 1Gi" ) - is an optional field that specifies how much computational resources to request or to limit for each of the broker pods.

spec.topology.controller

controller represents configuration for controllers of Kafka. In KRaft Topology mode clustering each pod can act as a single dedicated Kafka controller that preserves metadata for the whole cluster and participated in leader election.

Available configurable fields:

• topology.controller:
  • replicas (: "1") - is an optional field to specify the number of nodes (ie. pods ) that act as the dedicated Kafka controller pods. Defaults to 1.
  • suffix (: "controller") - is an optional field that is added as the suffix of the controller PetSet name. Defaults to controller.
  • storage is a required field that specifies how much storage to claim for each of the controller pods.
  • resources (: "cpu: 500m, memory: 1Gi" ) - is an optional field that specifies how much computational resources to request or to limit for each of the controller pods.

spec.enableSSL

spec.enableSSL is an optional field that specifies whether to enable TLS to HTTP layer. The default value of this field is false.

spec:
  enableSSL: true 

spec.tls

spec.tls specifies the TLS/SSL configurations. The KubeDB operator supports TLS management by using the cert-manager. Currently, the operator only supports the PKCS#8 encoded certificates.

spec:
  tls:
    issuerRef:
      apiGroup: "cert-manager.io"
      kind: Issuer
      name: kf-issuer
    certificates:
    - alias: server
      privateKey:
        encoding: PKCS8
      secretName: kf-client-cert
      subject:
        organizations:
        - kubedb
    - alias: http
      privateKey:
        encoding: PKCS8
      secretName: kf-server-cert
      subject:
        organizations:
        - kubedb

The spec.tls contains the following fields:

• tls.issuerRef - is an optional field that references to the Issuer or ClusterIssuer custom resource object of cert-manager. It is used to generate the necessary certificate secrets for Kafka. If the issuerRef is not specified, the operator creates a self-signed CA and also creates necessary certificate (valid: 365 days) secrets using that CA.

  • apiGroup - is the group name of the resource that is being referenced. Currently, the only supported value is cert-manager.io.
  • kind - is the type of resource that is being referenced. The supported values are Issuer and ClusterIssuer.
  • name - is the name of the resource ( Issuer or ClusterIssuer ) that is being referenced.

• tls.certificates - is an optional field that specifies a list of certificate configurations used to configure the certificates. It has the following fields:

  • alias - represents the identifier of the certificate. It has the following possible value:

    • server - is used for the server certificate configuration.
    • client - is used for the client certificate configuration.

  • secretName - ( string | "<database-name>-alias-cert" ) - specifies the k8s secret name that holds the certificates.

  • subject - specifies an X.509 distinguished name (DN). It has the following configurable fields:

    • organizations ( []string | nil ) - is a list of organization names.
    • organizationalUnits ( []string | nil ) - is a list of organization unit names.
    • countries ( []string | nil ) - is a list of country names (ie. Country Codes).
    • localities ( []string | nil ) - is a list of locality names.
    • provinces ( []string | nil ) - is a list of province names.
    • streetAddresses ( []string | nil ) - is a list of street addresses.
    • postalCodes ( []string | nil ) - is a list of postal codes.
    • serialNumber ( string | "" ) is a serial number.

    For more details, visit here.

  • duration ( string | "" ) - is the period during which the certificate is valid. A duration string is a possibly signed sequence of decimal numbers, each with optional fraction and a unit suffix, such as "300m", "1.5h" or "20h45m". Valid time units are “ns”, “us” (or “µs”), “ms”, “s”, “m”, “h”.

  • renewBefore ( string | "" ) - is a specifiable time before expiration duration.

  • dnsNames ( []string | nil ) - is a list of subject alt names.

  • ipAddresses ( []string | nil ) - is a list of IP addresses.

  • uris ( []string | nil ) - is a list of URI Subject Alternative Names.

  • emailAddresses ( []string | nil ) - is a list of email Subject Alternative Names.

spec.storageType

spec.storageType is an optional field that specifies the type of storage to use for database. It can be either Durable or Ephemeral. The default value of this field is Durable. If Ephemeral is used then KubeDB will create Kafka cluster using emptyDir volume.

spec.storage

If you set spec.storageType: to Durable, then spec.storage is a required field that specifies the StorageClass of PVCs dynamically allocated to store data for the database. This storage spec will be passed to the PetSet created by KubeDB operator to run database pods. You can specify any StorageClass available in your cluster with appropriate resource requests.

• spec.storage.storageClassName is the name of the StorageClass used to provision PVCs. PVCs don’t necessarily have to request a class. A PVC with its storageClassName set equal to "" is always interpreted to be requesting a PV with no class, so it can only be bound to PVs with no class (no annotation or one set equal to “”). A PVC with no storageClassName is not quite the same and is treated differently by the cluster depending on whether the DefaultStorageClass admission plugin is turned on.
• spec.storage.accessModes uses the same conventions as Kubernetes PVCs when requesting storage with specific access modes.
• spec.storage.resources can be used to request specific quantities of storage. This follows the same resource model used by PVCs.

To learn how to configure spec.storage, please visit the links below:

• https://kubernetes.io/docs/concepts/storage/persistent-volumes/#persistentvolumeclaims

NB. If spec.topology is set, then spec.storage needs to be empty. Instead use spec.topology.<controller/broker>.storage

spec.monitor

Kafka managed by KubeDB can be monitored with Prometheus operator out-of-the-box. To learn more,

• Monitor Apache with Prometheus operator

spec.podTemplate

KubeDB allows providing a template for database pod through spec.podTemplate. KubeDB operator will pass the information provided in spec.podTemplate to the PetSet created for Kafka cluster.

KubeDB accept following fields to set in spec.podTemplate:

• metadata:
  • annotations (pod’s annotation)
  • labels (pod’s labels)
• controller:
  • annotations (petset’s annotation)
  • labels (petset’s labels)
• spec:
  • resources
  • initContainers
  • containers
  • imagePullSecrets
  • nodeSelector
  • affinity
  • serviceAccountName
  • schedulerName
  • tolerations
  • priorityClassName
  • priority
  • securityContext
  • livenessProbe
  • readinessProbe
  • lifecycle

You can check out the full list here. Uses of some field of spec.podTemplate is described below,

NB. If spec.topology is set, then spec.podTemplate needs to be empty. Instead use spec.topology.<controller/broker>.podTemplate

spec.podTemplate.spec.nodeSelector

spec.podTemplate.spec.nodeSelector is an optional field that specifies a map of key-value pairs. For the pod to be eligible to run on a node, the node must have each of the indicated key-value pairs as labels (it can have additional labels as well). To learn more, see here .

spec.podTemplate.spec.resources

spec.podTemplate.spec.resources is an optional field. This can be used to request compute resources required by the database pods. To learn more, visit here.

spec.serviceTemplates

You can also provide template for the services created by KubeDB operator for Kafka cluster through spec.serviceTemplates. This will allow you to set the type and other properties of the services.

KubeDB allows following fields to set in spec.serviceTemplates:

• alias represents the identifier of the service. It has the following possible value:
  • stats is used for the exporter service identification.
• metadata:
  • labels
  • annotations
• spec:
  • type
  • ports
  • clusterIP
  • externalIPs
  • loadBalancerIP
  • loadBalancerSourceRanges
  • externalTrafficPolicy
  • healthCheckNodePort
  • sessionAffinityConfig

See here to understand these fields in detail.

spec.deletionPolicy

deletionPolicy gives flexibility whether to nullify(reject) the delete operation of Kafka crd or which resources KubeDB should keep or delete when you delete Kafka crd. KubeDB provides following four deletion policies:

• DoNotTerminate
• WipeOut
• Halt
• Delete

When deletionPolicy is DoNotTerminate, KubeDB takes advantage of ValidationWebhook feature in Kubernetes 1.9.0 or later clusters to implement DoNotTerminate feature. If admission webhook is enabled, DoNotTerminate prevents users from deleting the database as long as the spec.deletionPolicy is set to DoNotTerminate.

spec.healthChecker

It defines the attributes for the health checker.

• spec.healthChecker.periodSeconds specifies how often to perform the health check.
• spec.healthChecker.timeoutSeconds specifies the number of seconds after which the probe times out.
• spec.healthChecker.failureThreshold specifies minimum consecutive failures for the healthChecker to be considered failed.
• spec.healthChecker.disableWriteCheck specifies whether to disable the writeCheck or not.

Know details about KubeDB Health checking from this blog post.

Next Steps

• Learn how to use KubeDB to run Apache Kafka cluster here.
• Deploy dedicated topology cluster for Apache Kafka
• Deploy combined cluster for Apache Kafka
• Monitor your Kafka cluster with KubeDB using out-of-the-box Prometheus operator.
• Detail concepts of KafkaVersion object.
• Learn to use KubeDB managed Kafka objects using CLIs.
• Want to hack on KubeDB? Check our contribution guidelines.