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Druid

What is Druid

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

Druid Spec

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

apiVersion: kubedb.com/v1alpha2
kind: Druid
metadata:
  name: druid
  namespace: demo
spec:
  deepStorage:
    type: s3
    configSecret:
      name: deep-storage-config
  metadataStorage:
    type: PostgreSQL
    name: pg-demo
    namespace: demo
    externallyManaged: true
  zookeeperRef:
    name: zk-demo
    namespace: demo
    externallyManaged: true
  authSecret:
    name: druid-admin-cred
  configSecret:
    name: druid-custom-config
  enableSSL: true
  healthChecker:
    failureThreshold: 3
    periodSeconds: 20
    timeoutSeconds: 10
  keystoreCredSecret:
    name: druid-keystore-cred
  deletionPolicy: DoNotTerminate
  tls:
    certificates:
      - alias: server
        secretName: druid-server-cert
      - alias: client
        secretName: druid-client-cert
    issuerRef:
      apiGroup: cert-manager.io
      kind: Issuer
      name: druid-ca-issuer
  topology:
    coordinators:
      podTemplate:
        spec:
          containers:
            - name: druid
              resources:
                requests:
                  cpu: 500m
                  memory: 1024Mi
                limits:
                  cpu: 700m
                  memory: 2Gi
    overlords:
      podTemplate:
        spec:
          containers:
            - name: druid
              resources:
                requests:
                  cpu: 500m
                  memory: 1024Mi
                limits:
                  cpu: 700m
                  memory: 2Gi
    brokers:
      podTemplate:
        spec:
          containers:
            - name: druid
              resources:
                requests:
                  cpu: 500m
                  memory: 1024Mi
                limits:
                  cpu: 700m
                  memory: 2Gi
    routers:
      podTemplate:
        spec:
          containers:
            - name: druid
              resources:
                requests:
                  cpu: 500m
                  memory: 1024Mi
                limits:
                  cpu: 700m
                  memory: 2Gi
    middleManagers:
      podTemplate:
        spec:
          containers:
            - name: druid
              resources:
                requests:
                  cpu: 500m
                  memory: 1024Mi
                limits:
                  cpu: 700m
                  memory: 2Gi
      storageType: Durable
      storage:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 10Gi
        storageClassName: standard
    historicals:
      podTemplate:
        spec:
          containers:
            - name: druid
              resources:
                requests:
                  cpu: 500m
                  memory: 1024Mi
                limits:
                  cpu: 700m
                  memory: 2Gi
      storageType: Durable
      storage:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 10Gi
        storageClassName: standard
  monitor:
    agent: prometheus.io/operator
    prometheus:
      exporter:
        port: 56790
      serviceMonitor:
        labels:
          release: prometheus
        interval: 10s
  version: 30.0.1

spec.version

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

28.0.1
30.0.1
31.0.1

spec.replicas

spec.replicas the number of members in Druid 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 druid admin user. If not set, KubeDB operator creates a new Secret {druid-object-name}-auth for storing the password for admin user for each Druid object.

We can use this field in 3 mode.

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 Druid object using spec.authSecret.name & set spec.authSecret.externallyManaged to true.

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

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

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

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 Druid admin user.

Example:

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

apiVersion: v1
data:
  password: NnE4dV8yak1PVy1PT1pYaw==
  username: amhvbi1kb2U=
kind: Secret
metadata:
  name: druid-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 Druid configuration. If not set, KubeDB operator will use default configuration for Druid.

spec.topology

spec.topology represents the topology configuration for Druid 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.coordinators

coordinators represents configuration for coordinators node of Druid. It is a mandatory node. So, if not mentioned in the YAML, this node will be initialized by KubeDB operator.