New to KubeDB? Please start here.

SchemaRegistry

What is SchemaRegistry

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

SchemaRegistry Spec

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

apiVersion: kafka.kubedb.com/v1alpha1
kind: SchemaRegistry
metadata:
  name: schemaregistry
  namespace: demo
spec:
  version: 2.5.11.final
  healthChecker:
    failureThreshold: 3
    periodSeconds: 20
    timeoutSeconds: 10
  replicas: 3
  kafkaRef:
    name: kafka
    namespace: demo
  podTemplate:
    metadata:
      annotations:
        passMe: ToDatabasePod
      labels:
        thisLabel: willGoToPod
    controller:
      annotations:
        passMe: ToPetSet
      labels:
        thisLabel: willGoToSts
  deletionPolicy: WipeOut

spec.version

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

• 2.5.11.final
• 3.15.0

spec.replicas

spec.replicas the number of instances in SchemaRegistry.

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

spec.kafkaRef

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

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

spec.podTemplate

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

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:
  • 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.deletionPolicy

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

• Delete
• DoNotTerminate
• WipeOut

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 a Apache Kafka Connect cluster here.
• Monitor your SchemaRegistry 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.