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ConnectCluster

What is ConnectCluster

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

ConnectCluster Spec

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

apiVersion: kafka.kubedb.com/v1alpha1
kind: ConnectCluster
metadata:
  name: connectcluster
  namespace: demo
spec:
  version: 3.6.1
  healthChecker:
    failureThreshold: 3
    periodSeconds: 20
    timeoutSeconds: 10
  disableSecurity: false
  authSecret:
    name: connectcluster-auth
  enableSSL: true
  keystoreCredSecret:
    name: connectcluster-keystore-cred
  tls:
    issuerRef:
      apiGroup: cert-manager.io
      kind: Issuer
      name: connectcluster-ca-issuer
    certificates:
      - alias: server
        secretName: connectcluster-server-cert
      - alias: client
        secretName: connectcluster-client-cert
  configSecret:
    name: custom-connectcluster-config
  replicas: 3
  connectorPlugins:
    - gcs-0.13.0
    - mongodb-1.11.0
    - mysql-2.4.2.final
    - postgres-2.4.2.final
    - s3-2.15.0
    - jdbc-2.6.1.final
  kafkaRef:
    name: kafka
    namespace: demo
  podTemplate:
    metadata:
      annotations:
        passMe: ToDatabasePod
      labels:
        thisLabel: willGoToPod
    controller:
      annotations:
        passMe: ToStatefulSet
      labels:
        thisLabel: willGoToSts
  monitor:
    agent: prometheus.io/operator
    prometheus:
      exporter:
        port: 56790
      serviceMonitor:
        labels:
          release: prometheus
        interval: 10s
  terminationPolicy: WipeOut

spec.version

spec.version is a required field specifying the name of the KafkaVersion CR where the docker images are specified. Currently, when you install KubeDB, it creates the following KafkaVersion 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 worker nodes in ConnectCluster.

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

spec.disableSecurity

spec.disableSecurity is an optional field that specifies whether to disable all kind of security features like basic authentication and tls. The default value of this field is false.

spec.connectorPlugins

spec.connectorPlugins is an optional field that specifies the list of connector plugins to be installed in the ConnectCluster worker node. The field takes a list of strings where each string represents the name of the KafkaConnectorVersion CR. To learn more about KafkaConnectorVersion CR, visit here.

connectorPlugins:
  - <connector-plugin-name-1>
  - <connector-plugin-name-2>

spec.kafkaRef

spec.kafkaRef is a required field that specifies the name and namespace of the appbinding for Kafka object that the ConnectCluster object is associated with.

kafkaRef:
  name: <kafka-object-appbinding-name>
  namespace: <kafka-object-appbinding-namespace>

spec.configSecret

spec.configSecret is an optional field that specifies the name of the secret containing the custom configuration for the ConnectCluster. The secret should contain a key config.properties which contains the custom configuration for the ConnectCluster. The default value of this field is nil.

configSecret:
  name: <custom-config-secret-name>

spec.authSecret

spec.authSecret is an optional field that points to a Secret used to hold credentials for ConnectCluster username and password. If not set, KubeDB operator creates a new Secret {connectcluster-object-name}-connect-cred for storing the username and password for each ConnectCluster 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 ConnectCluster 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 ConnectCluster user.

Example:

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

apiVersion: v1
data:
  password: NnE4dV8yak1PVy1PT1pYaw==
  username: amhvbi1kb2U=
kind: Secret
metadata:
  name: kcc-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.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.keystoreCredSecret

spec.keystoreCredSecret is an optional field that specifies the name of the secret containing the keystore credentials for the ConnectCluster. The secret should contain three keys ssl.keystore.password, ssl.key.password and ssl.keystore.password. The default value of this field is nil.

spec:
  keystoreCredSecret:
    name: <keystore-cred-secret-name>

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: kcc-issuer
    certificates:
    - alias: server
      privateKey:
        encoding: PKCS8
      secretName: kcc-client-cert
      subject:
        organizations:
        - kubedb
    - alias: http
      privateKey:
        encoding: PKCS8
      secretName: kcc-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 ConnectCluster. 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.monitor

ConnectCluster 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 pod through spec.podTemplate. KubeDB operator will pass the information provided in spec.podTemplate to the StatefulSet created for ConnectCluster.

KubeDB accept following fields to set in spec.podTemplate:

• metadata:
  • annotations (pod’s annotation)
  • labels (pod’s labels)
• controller:
  • annotations (statefulset’s annotation)
  • labels (statefulset’s labels)
• spec:
  • volumes
  • 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,

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.terminationPolicy

spec.terminationPolicy gives flexibility whether to nullify(reject) the delete operation of ConnectCluster crd or which resources KubeDB should keep or delete when you delete ConnectCluster crd. KubeDB provides following four termination policies:

• Delete
• DoNotTerminate
• WipeOut

When terminationPolicy 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.terminationPolicy 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 a Apache Kafka Connect cluster here.
• Monitor your ConnectCluster with KubeDB using out-of-the-box Prometheus operator.
• Detail concepts of KafkaConnectorVersion object.
• Learn to use KubeDB managed Kafka objects using CLIs.
• Want to hack on KubeDB? Check our contribution guidelines.