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RedisSentinel

What is RedisSentinel

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

RedisSentinel Spec

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

apiVersion: kubedb.com/v1alpha2
kind: RedisSentinel
metadata:
  name: sentinel1
  namespace: demo
spec:
  autoOps:
    disabled: true
  version: 6.2.14
  replicas: 3
  disableAuth: false
  authSecret:
    name: sentinel1-auth
    externallyManaged: false
  tls:
    issuerRef:
      name: redis-ca-issuer
      kind: ClusterIssuer
      apiGroup: "cert-manager.io"
    certificates:
      - alias: client
        subject:
          organizations:
            - kubedb
        emailAddresses:
          - [email protected]
      - alias: server
        subject:
          organizations:
            - kubedb
        emailAddresses:
          - [email protected]
  storage:
    storageClassName: "standard"
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  monitor:
    agent: prometheus.io/operator
    prometheus:
      serviceMonitor:
        labels:
          app: kubedb
        interval: 10s
  podTemplate:
    metadata:
      annotations:
        passMe: ToDatabasePod
    controller:
      annotations:
        passMe: ToStatefulSet
    spec:
      serviceAccountName: my-service-account
      imagePullSecrets:
        - name: regcred
      args:
        - "--loglevel verbose"
      env:
        - name: ENV_VARIABLE
          value: "value"
      resources:
        requests:
          memory: "64Mi"
          cpu: "250m"
        limits:
          memory: "128Mi"
          cpu: "500m"
  serviceTemplates:
    - alias: primary
      metadata:
        annotations:
          passMe: ToService
      spec:
        type: NodePort
        ports:
          - name:  http
            port:  9200
  terminationPolicy: Halt
  halted: false
  healthChecker:
    periodSeconds: 15
    timeoutSeconds: 10
    failureThreshold: 2
    disableWriteCheck: false

spec.autoOps

AutoOps is an optional field to control the generation of version update & TLS-related recommendations.

spec.version

spec.version is a required field specifying the name of the RedisVersion crd where the docker images are specified. RedisSentinel is supported in following Redis Versions.

• 6.2.14, 6.2.14 6.2.14
• 7.0.4, 7.0.14, 7.0.6

spec.disableAuth

spec.disableAuth is an optional field that decides whether RedisSentinel instance will be secured by auth or no.

spec.authSecret

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

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 RedisSentinel 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 RedisSentinel 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 redis superuser.

Example:

$ kubectl create secret generic sentinel1-auth -n demo \
--from-literal=username=jhon-doe \
--from-literal=password=6q8u_2jMOW-OOZXk
secret "sentinel1-auth" created

apiVersion: v1
data:
  password: NnE4dV8yak1PVy1PT1pYaw==
  username: amhvbi1kb2U=
kind: Secret
metadata:
  name: sentinel1-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.tls

spec.tls specifies the TLS/SSL configurations for the RedisSentinel. KubeDB uses cert-manager v1 api to provision and manage TLS certificates.

The following fields are configurable in the spec.tls section:

• issuerRef is a reference to the Issuer or ClusterIssuer CR of cert-manager that will be used by KubeDB to generate necessary certificates.

  • 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. KubeDB supports both Issuer and ClusterIssuer as values for this field.
  • name is the name of the resource (Issuer or ClusterIssuer) being referenced.

• certificates (optional) are a list of certificates used to configure the server and/or client certificate. It has the following fields:

  • alias represents the identifier of the certificate. It has the following possible value:
    • server is used for server certificate identification.
    • client is used for client certificate identification.
    • metrics-exporter is used for metrics exporter certificate identification.
  • secretName (optional) specifies the k8s secret name that holds the certificates.

This field is optional. If the user does not specify this field, the default secret name will be created in the following format: <database-name>-<cert-alias>-cert.

• subject (optional) specifies an X.509 distinguished name. It has the following possible field,
  • organizations (optional) are the list of different organization names to be used on the Certificate.
  • organizationalUnits (optional) are the list of different organization unit name to be used on the Certificate.
  • countries (optional) are the list of country names to be used on the Certificate.
  • localities (optional) are the list of locality names to be used on the Certificate.
  • provinces (optional) are the list of province names to be used on the Certificate.
  • streetAddresses (optional) are the list of a street address to be used on the Certificate.
  • postalCodes (optional) are the list of postal code to be used on the Certificate.
  • serialNumber (optional) is a serial number to be used on the Certificate. You can find more details from Here
• duration (optional) is the period during which the certificate is valid.
• renewBefore (optional) is a specifiable time before expiration duration.
• dnsNames (optional) is a list of subject alt names to be used in the Certificate.
• ipAddresses (optional) is a list of IP addresses to be used in the Certificate.
• uris (optional) is a list of URI Subject Alternative Names to be set in the Certificate.
• emailAddresses (optional) is a list of email Subject Alternative Names to be set in the Certificate.
• privateKey (optional) specifies options to control private keys used for the Certificate.
  • encoding (optional) is the private key cryptography standards (PKCS) encoding for this certificate’s private key to be encoded in. If provided, allowed values are “pkcs1” and “pkcs8” standing for PKCS#1 and PKCS#8, respectively. It defaults to PKCS#1 if not specified.

The Redis object we construct will be watched over by the Redis Sentinel object, therefore in order for them to connect in TLS enabled mode, both objects must have the same issuer. On the other side, the Redis object must likewise be TLS off if the RedisSentinel object is. Set spec.tls.issuerRef.kind to ClusterIssuer if you want your RedisSentinel object and Redis object to be in different namespaces. Both “Issuer” and “ClusterIssuer” can be used if both instances are in the same namespace.

spec.storage

Since 0.10.0-rc.0, 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 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.monitor

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

• Monitor Redis with builtin Prometheus
• Monitor Redis 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 StatefulSet created for RedisSentinel server.

KubeDB accept following fields to set in spec.podTemplate:

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

Uses of some field of spec.podTemplate is described below,

spec.podTemplate.spec.args

spec.podTemplate.spec.args is an optional field. This can be used to provide additional arguments to database installation.

spec.podTemplate.spec.env

spec.podTemplate.spec.env is an optional field that specifies the environment variables to pass to the Redis docker image.

Note that, KubeDB does not allow to update the environment variables. 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: "./redis.yaml": admission webhook "redis.validators.kubedb.com" denied the request: precondition failed for:
...
At least one of the following was changed:
apiVersion
kind
name
namespace
spec.storage
spec.podTemplate.spec.nodeSelector
spec.podTemplate.spec.env

spec.podTemplate.spec.imagePullSecret

KubeDB provides the flexibility of deploying Redis server from a private Docker registry. To learn how to deploy Redis from a private 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.serviceAccountName

serviceAccountName is an optional field supported by KubeDB Operator (version 0.13.0 and higher) that can be used to specify a custom service account to fine tune role based access control.

If this field is left empty, the KubeDB operator will create a service account name matching RedisSentinel crd name. Role and RoleBinding that provide necessary access permissions will also be generated automatically for this service account.

If a service account name is given, but there’s no existing service account by that name, the KubeDB operator will create one, and Role and RoleBinding that provide necessary access permissions will also be generated for this service account.

If a service account name is given, and there’s an existing service account by that name, the KubeDB operator will use that existing service account. Since this service account is not managed by KubeDB, users are responsible for providing necessary access permissions manually. Follow the guide here to grant necessary permissions in this scenario.

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 a template for the services created by KubeDB operator for Redis server 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:

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

See here to understand these fields in detail.

spec.terminationPolicy

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

• DoNotTerminate
• Halt
• Delete (Default)
• 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.

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

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

spec.halted

Indicates that the database is halted and all offshoot Kubernetes resources except PVCs are deleted.

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.

Sample Redis instace

A yaml for a sample Redis instance that can be monitored by this RedisSentinel instance is given below

apiVersion: kubedb.com/v1alpha2
kind: Redis
metadata:
  name: redis1
  namespace: demo
spec:
  version: 6.2.14
  replicas: 3
  sentinelRef:
    name: sentinel1
    namespace: demo
  mode: Sentinel
  tls:
    issuerRef:
      apiGroup: cert-manager.io
      name: redis-ca-issuer
      kind: ClusterIssuer
    certificates:
      - alias: server
        subject:
          organizations:
            - kubedb:server
        dnsNames:
          - localhost
        ipAddresses:
          - "127.0.0.1"
  storageType: Durable
  storage:
    resources:
      requests:
        storage: 1Gi
    storageClassName: "standard"
    accessModes:
      - ReadWriteOnce
  terminationPolicy: WipeOut

Next Steps

• Learn how to use KubeDB to run a Redis server here.
• Want to hack on KubeDB? Check our contribution guidelines.