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Elasticsearch

What is Elasticsearch

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

Elasticsearch Spec

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

apiVersion: kubedb.com/v1alpha1
kind: Elasticsearch
metadata:
  name: e1
  namespace: demo
spec:
  version: "6.3-v1"
  replicas: 2
  authPlugin: "SearchGuard"
  enableSSL: true
  certificateSecret:
    secretName: e1-certs
  databaseSecret:
    secretName: e1-auth
  storageType: "Durable"
  storage:
    storageClassName: standard
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 50Mi
  init:
    scriptSource:
      configMap:
        name: es-init-script
  backupSchedule:
    cronExpression: "@every 6h"
    storageSecretName: gcs-secret
    gcs:
      bucket: kubedb
      prefix: demo
  monitor:
    agent: prometheus.io/coreos-operator
    prometheus:
      namespace: demo
      labels:
        app: kubedb
      interval: 10s
  configSource:
    configMap:
      name: es-custom-config
  podTemplate:
    annotation:
      passMe: ToDatabasePod
    controller:
      annotation:
        passMe: ToStatefulSet
    spec:
      schedulerName: my-scheduler
      nodeSelector:
        disktype: ssd
      imagePullSecrets:
      - name: myregistrykey
      env:
      - name: ES_JAVA_OPTS
        value: "-Xms128m -Xmx128m"
      resources:
        requests:
          memory: "64Mi"
          cpu: "250m"
        limits:
          memory: "128Mi"
          cpu: "500m"
  serviceTemplate:
    annotation:
      passMe: ToService
    spec:
      type: NodePort
      ports:
      - name:  http
        port:  9200
        targetPort: http
  updateStrategy:
    type: "RollingUpdate"
  terminationPolicy: "DoNotTerminate"

spec.version

spec.version is a required field that specifies the name of the ElasticsearchVersion crd where the docker images are specified. Currently, when you install KubeDB, it creates the following ElasticsearchVersion crd,

• 5.6, 5.6-v1, 5.6.4, 5.6.4-v1
• 6.2, 6.2-v1, 6.2.4, 6.2.4-v1, 6.3, 6.3-v1, 6.3.0, 6.3.0-v1

spec.topology

spec.topology is an optional field that provides a way to configure different types of nodes for Elasticsearch cluster. This field enables you to specify how many nodes you want to act as master, data and client node. You can also specify how much storage and resources to use for each types of nodes independently.

You can specify the following things in spec.topology field,

• spec.topology.master
  • .replicas is an optional field to specify how many pods we want as master node. If not set, this defaults to 1.
  • .prefix is an optional field to be used as the prefix of StatefulSet name.
  • .storage is an optional field that specifies how much storage to use for master node.
  • .resources is an optional field that specifies how much compute resources to request for master node.
• spec.topology.data
  • .replicas is an optional field to specify how many pods we want as data node. If not set, this defaults to 1.
  • .prefix is an optional field to be used as the prefix of StatefulSet name.
  • .storage is an optional field that specifies how much storage to use for data node.
  • .resources is an optional field that specifies how much compute resources to request for data node.
• spec.topology.client
  • .replicas is an optional field to specify how many pods we want as client node. If not set, this defaults to 1.
  • .prefix is an optional field to be used as the prefix of StatefulSet name.
  • .storage is an optional field that specifies how much storage to use for client node.
  • .resources is an optional field that specifies how much compute resources to request for client node.

Note: Any two of them can’t have the same prefix.

A sample configuration for spec.topology field is shown below,

topology:
  master:
    prefix: master
    replicas: 1
    storage:
      storageClassName: "standard"
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 1Gi
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"
  data:
    prefix: data
    replicas: 3
    storage:
      storageClassName: "standard"
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 1Gi
    resources:
      requests:
        memory: "512Mi"
        cpu: "250m"
      limits:
        memory: "1Gi"
        cpu: "500m"
  client:
    prefix: client
    replicas: 2
    storage:
      storageClassName: "standard"
      accessModes:
      - ReadWriteOnce
      resources:
        requests:
          storage: 50Mi
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"

If you specify spec.topology field then you are not allowed to specify following fields in Elasticsearch crd.

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

If you do not specify spec.topology field, all nodes of your Elasticsearch cluster will work as master, data and client node simultaneously.

spec.replicas

spec.replicas is an optional field that can be used if spec.topology is not specified. This field specifies the number of pods in the Elasticsearch cluster. The default value of this field is 1.

spec.authPlugin

spec.authPlugin is an optional field that specifies which plugin to use for authentication. Currently, this field accepts None or SearchGuard. By default, KubeDB uses Search Guard for authentication. If you specify None in this field, KubeDB will disable Search Guard plugin and your database will not be protected anymore.

spec.enableSSL

spec.enableSSL is an optional field that specifies whether to enable SSL for Search Guard. The default value of this field is false.

spec.certificateSecret

spec.certificateSecret is an optional field that points a Secret used to hold the following information for the certificate.

• root.pem: The root CA in pem format
• root.jks: The root CA in jks format
• node.jks: The node certificate used for the transport layer
• client.jks: The client certificate used for http layer
• sgadmin.jks: The admin certificate used to change the Search Guard configuration.
• key_pass: The key password used to encrypt certificates.

If not set, KubeDB operator creates a new Secret {Elasticsearch name}-cert with generated certificates. If you want to use an existing secret, please specify that when creating Elasticsearch using spec.certificateSecret.secretName.

spec.databaseSecret

spec.databaseSecret is an optional field that points to a Secret used to hold credentials and search guard configuration.

Following keys are used to hold credentials

• ADMIN_USERNAME: Username for superuser.
• ADMIN_PASSWORD: Password for superuser.
• READALL_USERNAME Username for readall user.
• READALL_PASSWORD: Password for readall user.

Following keys are used for search-guard configuration

• sg_config.yml: Configure authenticators and authorization backends
• sg_internal_users.yml: user and hashed passwords (hash with hasher.sh)
• sg_roles_mapping.yml: map backend roles, hosts and users to roles
• sg_action_groups.yml: define permission groups
• sg_roles.yml: define the roles and the associated permissions

If not set, KubeDB operator creates a new Secret {Elasticsearch name}-auth with generated credentials and default search-guard configuration. If you want to use an existing secret, please specify that when creating Elasticsearch using spec.databaseSecret.secretName.

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 Elasticsearch database using emptyDir volume. In this case, you don’t have to specify spec.storage field.

spec.storage

If you don’t set spec.storageType: to Ephemeral and if you don’t specify spec.topology filed then spec.storage field is required. This field specifies the StorageClass of PVCs dynamically allocated to store data for the database. This storage spec will be passed to the StatefulSet 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

spec.init

spec.init is an optional section that can be used to initialize a newly created Elasticsearch cluster from prior snapshots. To initialize from prior snapshots, set the spec.init.snapshotSource section when creating an Elasticsearch object. In this case, SnapshotSource must have the following information:

• name: Name of the Snapshot
• namespace: Namespace of the Snapshot

apiVersion: kubedb.com/v1alpha1
kind: Elasticsearch
metadata:
  name: elasticsearch-db
spec:
  version: "5.6-v1"
  databaseSecret:
    secretName: old-elasticsearch-auth
  init:
    snapshotSource:
      name: "snapshot-xyz"
      namespace: demo

In the above example, Elasticsearch cluster will be initialized from Snapshot snapshot-xyz in demo namespace. Here, KubeDB operator will launch a Job to initialize Elasticsearch, once StatefulSet pods are running. For details tutorial on how to initialize Elasticsearch from snapshot, please visit here.

spec.backupSchedule

KubeDB supports taking periodic snapshots for Elasticsearch database. This is an optional section in .spec. When spec.backupSchedule section is added, KubeDB operator immediately takes a backup to validate this information. After that, at each tick kubeDB operator creates a Snapshot object. This triggers operator to create a Job to take backup.

You have to specify following fields to take periodic backup of your Elasticsearch database:

• spec.backupSchedule.cronExpression is a required cron expression. This specifies the schedule for backup operations.
• spec.backupSchedule.{storage} is a required field that is used as the destination for storing snapshot data. KubeDB supports cloud storage providers like S3, GCS, Azure, and OpenStack Swift. It also supports any locally mounted Kubernetes volumes, like NFS, Ceph, etc. Only one backend can be used at a time. To learn how to configure this, please visit here.

You can also specify a template for pod of backup job through spec.backupSchedule.podTemplate. KubeDB will use the information you have provided in podTemplate to create the backup job. KubeDB accept following fields to set in spec.backupSchedule.podTemplate:

• metadata
  • annotations (pod’s annotation)
• controller
  • annotations (job’s annotation)
• spec:
  • args
  • env
  • resources
  • imagePullSecrets
  • initContainers
  • nodeSelector
  • affinity
  • schedulerName
  • tolerations
  • priorityClassName
  • priority
  • securityContext
  • livenessProbe
  • readinessProbe
  • lifecycle

spec.monitor

Elasticsearch managed by KubeDB can be monitored with builtin-Prometheus and CoreOS-Prometheus operator out-of-the-box. To learn more,

• Monitor Elasticsearch with builtin Prometheus
• Monitor Elasticsearch with CoreOS Prometheus operator

spec.configSource

spec.configSource is an optional field that allows users to provide custom configuration for Elasticsearch. This field accepts a VolumeSource. So you can use any kubernetes supported volume source such as configMap, secret, azureDisk etc. To learn more about how to use a custom configuration file see here.

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 StatefulSet created for Elasticsearch database.

KubeDB accept following fields to set in spec.podTemplate:

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

Uses of some fields of spec.podTemplate are described below,

spec.podTemplate.spec.env

spec.podTemplate.spec.env is an optional field that specifies the environment variables to pass to the Elasticsearch docker image. To know about supported environment variables, please visit here.

A list of the supported environment variables, their permission to use in KubeDB and their default value is given below.

Note that, KubeDB does not allow NODE_NAME, NODE_MASTER, and NODE_DATA environment variables to set in spec.podTemplate.spec.env. KubeDB operator set them based on Elasticsearch crd specification.

If you try to set any these forbidden environment variable in Elasticsearch crd, KubeDB operator will reject the request with following error,

Error from server (Forbidden): error when creating "./elasticsearch.yaml": admission webhook "elasticsearch.validators.kubedb.com" denied the request: environment variable NODE_NAME is forbidden to use in Elasticsearch spec

Also, note that KubeDB does not allow to update the environment variables as updating them does not have any effect once the database is created. If you try to update environment variables, KubeDB operator will reject the request with following error,

Error from server (BadRequest): error when applying patch:
...
for: "./elasticsearch.yaml": admission webhook "elasticsearch.validators.kubedb.com" denied the request: precondition failed for:
...
At least one of the following was changed:
    apiVersion
    kind
    name
    namespace
    spec.version
    spec.topology.*.prefix
    spec.topology.*.storage
    spec.enableSSL
    spec.certificateSecret
    spec.databaseSecret
    spec.storageType
    spec.storage
    spec.nodeSelector
    spec.init
    spec.env

spec.podTemplate.spec.imagePullSecrets

spec.podTemplate.spec.imagePullSecrets is an optional field that points to secrets to be used for pulling docker image when you are using a private docker registry. For more details on how to use private docker registry, please visit here.

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. If you didn’t specify spec.topology field then this can be used to request compute resources required by the database pods. To learn more, visit here.

spec.serviceTemplate

You can also provide a template for the services created by KubeDB operator for Elasticsearch database through spec.serviceTemplate. This will allow you to set the type and other properties of the services.

KubeDB allows following fields to set in spec.serviceTemplate:

• metadata:
  • annotations
• spec:
  • type
  • ports
  • clusterIP
  • externalIPs
  • loadBalancerIP
  • loadBalancerSourceRanges
  • externalTrafficPolicy
  • healthCheckNodePort

spec.updateStrategy

You can specify update strategy of StatefulSet created by KubeDB for Elasticsearch database thorough spec.updateStrategy field. The default value of this field is RollingUpdate. In future, we will use this field to determine how automatic migration from old KubeDB version to new one should behave.

spec.terminationPolicy

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

• DoNotTerminate
• Pause (Default)
• Delete
• WipeOut

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

Following table show what KubeDB does when you delete Elasticsearch crd for different termination policies,

If you don’t specify spec.terminationPolicy KubeDB uses Pause termination policy by default.

Next Steps

• Learn how to use KubeDB to run an Elasticsearch database here.
• See the list of supported storage providers for snapshots here.
• Want to hack on KubeDB? Check our contribution guidelines.