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What is Memcached

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

Memcached Spec

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

kind: Memcached
  name: mc1
  namespace: demo
  replicas: 3
  version: 1.5.3-v1
          app: kubedb
        interval: 10s
    name: mc-custom-config
      passMe: ToDatabasePod
        passMe: ToDeployment
      serviceAccountName: my-service-account
      schedulerName: my-scheduler
        disktype: ssd
      - name: myregistrykey
      - "-u memcache"
      - name: TEST_ENV
        value: "value"
          memory: "64Mi"
          cpu: "250m"
          memory: "128Mi"
          cpu: "500m"
      passMe: ToService
      type: NodePort
      - name:  http
        port:  9200
        targetPort: http
  terminationPolicy: Halt


spec.replicas is an optional field that specifies the number of desired Instances/Replicas of Memcached server. If you do not specify .spec.replicas, then it defaults to 1.

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


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

  • 1.5.4, 1.5.4-v1, 1.5, 1.5-v1


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


spec.configSecret is an optional field that allows users to provide custom configuration for Memcached. 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.


KubeDB allows providing a template for database pod through spec.podTemplate. KubeDB operator will pass the information provided in spec.podTemplate to the Deployment created for Memcached 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 is an optional field. This can be used to provide additional arguments to database installation.


spec.env is an optional field that specifies the environment variables to pass to the Memcached 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: "./mc.yaml": admission webhook "" denied the request: precondition failed for:
At least one of the following was changed:


KubeDB provides the flexibility of deploying Memcached server from a private Docker registry. To learn how to deploym Memcached from a private registry, please visit here.


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 .


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 Memcached 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.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 Memcached server 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
    • sessionAffinityConfig

See here to understand these fields in detail.


terminationPolicy gives flexibility whether to nullify(reject) the delete operation of Memcached crd or which resources KubeDB should keep or delete when you delete Memcached 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 Memcached crd for different termination policies,

1. Block Delete operation
2. Create Dormant Database
3. Delete StatefulSet
4. Delete Services

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

Next Steps