New to KubeDB? Please start here.
What is Redis
Redis 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 object, and the KubeDB operator will create Kubernetes objects in the desired state for you.
As with all other Kubernetes objects, a Redis needs
metadata fields. It also needs a
.spec section. Below is an example Redis object.
apiVersion: kubedb.com/v1alpha1 kind: Redis metadata: name: r1 namespace: demo spec: version: 4 storage: storageClassName: "standard" accessModes: - ReadWriteOnce resources: requests: storage: 50Mi monitor: agent: prometheus.io/coreos-operator prometheus: namespace: demo labels: app: kubedb interval: 10s configSource: configMap: name: rd-custom-config podTemplate: annotation: passMe: ToDatabasePod controller: annotation: passMe: ToStatefulSet spec: schedulerName: my-scheduler nodeSelector: disktype: ssd imagePullSecrets: - name: myregistrykey args: - "--loglevel verbose" env: - name: ENV_VARIABLE value: "value" 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 terminationPolicy: Pause updateStrategy: type: RollingUpdate
spec.version is a required field specifying the name of the RedisVersion crd where the docker images are specified. Currently, when you install KubeDB, it creates the following
Since 0.9.0-rc.0, If you set
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.storageClassNameis 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.accessModesuses the same conventions as Kubernetes PVCs when requesting storage with specific access modes.
spec.storage.resourcescan 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:
Redis managed by KubeDB can be monitored with builtin-Prometheus and CoreOS-Prometheus operator out-of-the-box. To learn more,
spec.configSource is an optional field that allows users to provide custom configuration for Redis. This field accepts a
VolumeSource. So you can use any kubernetes supported volume source such as
azureDisk etc. To learn more about how to use a custom configuration file see here.
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 Redis database.
KubeDB accept following fields to set in
- annotations (pod’s annotation)
- annotations (statefulset’s annotation)
Uses of some field of
spec.podTemplate is described below,
spec.podTemplate.spec.args is an optional field. This can be used to provide additional arguments to database installation.
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
KubeDB provides the flexibility of deploying Redis database from a private Docker registry. To learn how to deploy Redis from a private registry, please visit here.
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 is an optional field. This can be used to request compute resources required by the database pods. To learn more, visit here.
You can also provide a template for the services created by KubeDB operator for Redis 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
You can specify update strategy of StatefulSet created by KubeDB for Redis 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.
terminationPolicy gives flexibility whether to
nullify(reject) the delete operation of
Redis crd or which resources KubeDB should keep or delete when you delete
Redis crd. KubeDB provides following four termination policies:
- Pause (
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
Following table show what KubeDB does when you delete Redis crd for different termination policies,
|1. Block Delete operation||✓||✗||✗||✗|
|2. Create Dormant Database||✗||✓||✗||✗|
|3. Delete StatefulSet||✗||✓||✓||✓|
|4. Delete Services||✗||✓||✓||✓|
|5. Delete PVCs||✗||✗||✓||✓|
|6. Delete Secrets||✗||✗||✗||✓|
If you don’t specify
spec.terminationPolicy KubeDB uses
Pause termination policy by default.