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Memcached
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.
apiVersion: kubedb.com/v1alpha1
kind: Memcached
metadata:
name: mc1
namespace: demo
spec:
replicas: 3
version: 1.5.3-v1
monitor:
agent: coreos-prometheus-operator
prometheus:
namespace: demo
labels:
app: kubedb
interval: 10s
configSource:
configMap:
name: mc-custom-config
podTemplate:
annotations:
passMe: ToDatabasePod
controller:
annotations:
passMe: ToDeployment
spec:
schedulerName: my-scheduler
nodeSelector:
disktype: ssd
imagePullSecrets:
- name: myregistrykey
args:
- "-u memcache"
env:
- name: TEST_ENV
value: "value"
resources:
requests:
memory: "64Mi"
cpu: "250m"
limits:
memory: "128Mi"
cpu: "500m"
serviceTemplate:
annotations:
passMe: ToService
spec:
type: NodePort
ports:
- name: http
port: 9200
targetPort: http
terminationPolicy: Pause
updateStrategy:
type: RollingUpdate
spec.replicas
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.
spec.version
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
crd,
1.5.4
,1.5.4-v1
,1.5
,1.5-v1
spec.monitor
Memcached managed by KubeDB can be monitored with builtin-Prometheus and CoreOS-Prometheus operator out-of-the-box. To learn more,
spec.configSource
spec.configSource
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.
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 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
- 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.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 "memcached.validators.kubedb.com" denied the request: precondition failed for:
...
At least one of the following was changed:
apiVersion
kind
name
namespace
spec.podTemplate.spec.nodeSelector
spec.podTemplate.spec.env
spec.podTemplate.spec.imagePullSecrets
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.podTemplate.spec.nodeSelector
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.resources
is an optional field. 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 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
spec.updateStrategy
You can specify update strategy of Deployment created by KubeDB for Memcached server 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 Memcached
crd or which resources KubeDB should keep or delete when you delete Memcached
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 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,
Behaviour | DoNotTerminate | Pause | Delete | WipeOut |
---|---|---|---|---|
1. Block Delete operation | ✓ | ✗ | ✗ | ✗ |
2. Create Dormant Database | ✗ | ✓ | ✗ | ✗ |
3. Delete StatefulSet | ✗ | ✓ | ✓ | ✓ |
4. Delete Services | ✗ | ✓ | ✓ | ✓ |
If you don’t specify spec.terminationPolicy
KubeDB uses Pause
termination policy by default.
Next Steps
- Learn how to use KubeDB to run a Memcached server here.
- Want to hack on KubeDB? Check our contribution guidelines.