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Apply instance template

Instance template can be applied to many scenarios. In this section, we take RisingWave cluster as an example. KubeBlocks supports the management of RisingWave clusters. The RisingWave addon is contributed by the RisingWave official team. For RisingWave to function optimally, it relies on an external storage solution, such as AWS S3 or Alibaba Cloud OSS, to serve as its state backend. When creating a RisingWave cluster, it is necessary to configure credentials and other information for the external storage to ensure normal operation, and these information may vary for each cluster.

In the official image of RisingWave, these information can be injected via environment variables. Therefore, in KubeBlocks 0.9, we can configure corresponding environment variables in the instance template and set the values of these environment variables each time a cluster is created, so as to inject credential information into the container of RisingWave.

An example

In the default template of RisingWave addon, the environment viriables are configured as follows:

apiVersion: apps.kubeblocks.io/v1alpha1
kind: ClusterDefinition
metadata:
name: risingwave
# ...
spec:
componentDefs:
- name: compute
# ...
podSpec:
containers:
- name: compute
securityContext:
allowPrivilegeEscalation: false
capabilities:
drop:
- ALL
privileged: false
command:
- /risingwave/bin/risingwave
- compute-node
env:
- name: RUST_BACKTRACE
value: "1"
- name: RW_CONFIG_PATH
value: /risingwave/config/risingwave.toml
- name: RW_LISTEN_ADDR
value: 0.0.0.0:5688
- name: RW_ADVERTISE_ADDR
value: $(KB_POD_FQDN):5688
- name: RW_META_ADDR
value: load-balance+http://$(metaSvc)-headless:5690
- name: RW_METRICS_LEVEL
value: "1"
- name: RW_CONNECTOR_RPC_ENDPOINT
value: $(connectorSvc):50051
- name: RW_PROMETHEUS_LISTENER_ADDR
value: 0.0.0.0:1222
# ...

After adding an instance template to the cluster resources:

apiVersion: apps.kubeblocks.io/v1alpha1
kind: Cluster
metadata:
name: {{ include "risingwave-cluster.name" . }}
namespace: {{ .Release.Namespace }}
# ...
spec:
componentSpecs:
- componentDefRef: compute
name: compute
replicas: {{ .Values.risingwave.compute.replicas }}
instances:
- name: instance
replicas: {{ .Values.risingwave.compute.replicas }}
env:
- name: RW_STATE_STORE
value: "hummock+s3://{{ .Values.risingwave.stateStore.s3.bucket }}"
- name: AWS_REGION
value: "{{ .Values.risingwave.stateStore.s3.region }}"
{{- if eq .Values.risingwave.stateStore.s3.authentication.serviceAccountName "" }}
- name: AWS_ACCESS_KEY_ID
value: "{{ .Values.risingwave.stateStore.s3.authentication.accessKey }}"
- name: AWS_SECRET_ACCESS_KEY
value: "{{ .Values.risingwave.stateStore.s3.authentication.secretAccessKey }}"
{{- end }}
- name: RW_DATA_DIRECTORY
value: "{{ .Values.risingwave.stateStore.dataDirectory }}"
{{- if .Values.risingwave.stateStore.s3.endpoint }}
- name: RW_S3_ENDPOINT
value: "{{ .Values.risingwave.stateStore.s3.endpoint }}"
{{- end }}
{{- if .Values.risingwave.metaStore.etcd.authentication.enabled }}
- name: RW_ETCD_USERNAME
value: "{{ .Values.risingwave.metaStore.etcd.authentication.username }}"
- name: RW_ETCD_PASSWORD
value: "{{ .Values.risingwave.metaStore.etcd.authentication.password }}"
{{- end }}
- name: RW_ETCD_ENDPOINTS
value: "{{ .Values.risingwave.metaStore.etcd.endpoints }}"
- name: RW_ETCD_AUTH
value: "{{ .Values.risingwave.metaStore.etcd.authentication.enabled}}"
# ...

In the example above, we added an instance template through the instances field, named instance. This template defines several environment variables such as RW_STATE_STORE and AWS_REGION. These environment variables will be appended by KubeBlocks to the list of environment variables defined in the default template. Consequently, the rendered instance will contain both the default template and all the environment variables defined in this instance template.

Additionally, the replicas field in the instance template is identical to that in the componentSpec (both are {{ .Values.risingwave.compute.replicas }}), indicating that after overriding the default template, this instance template will be used to render all instances within this component.

Detailed information of instance template

  • Name field: For each component, multiple instance templates can be defined. Template name is configured with Name field, and must remain unique within the same component.
  • Replica field: Each template can set the number of instances rendered based on that template via the Replicas field, of which the default value is 1. The sum of Replicas for all instance templates within the same component must be less than or equal to the Replicas value of the component. If the number of instances rendered based on the instance templates is less than the total number required by the component, the remaining instances will be rendered using the default template.

The pattern for the names of instances rendered based on instance templates is $(cluster name)-$(component name)-$(instance template name)-ordinal. For example, in the above RisingWave cluster, the cluster name is risingwave, the component name is compute, the instance template name is instance, and the number of Replicas is 3. Therefore, the rendered instance names are: risingwave-compute-instance-0, risingwave-compute-instance-1, risingwave-compute-instance-2.

Instance templates can be used during cluster creation and can be updated during operations period. Specifically, this includes adding, deleting, or updating instance templates. Updating instance templates may update, delete, or reconstruct instances. You are recommended to carefully evaluate whether the final changes meet expectations before performing updates.

Annotations

The Annotations in the instance template are used to override the Annotations field in the default template. If a Key in the Annotations of the instance template already exists in the default template, the value corresponding to the Key will use the value in the instance template; if the Key does not exist in the default template, the Key and Value will be added to the final Annotations. Example: The annotations in the default template are:

annotations:
"foo0": "bar0"
"foo1": "bar"

And annotations in the instance templates are:

annotations:
"foo1": "bar1"
"foo2": "bar2"

Then, after rendering, the actual annotations are:

annotations:
"foo0": "bar0"
"foo1": "bar1"
"foo2": "bar2"

...note KubeBlocks adds system Annotations, and do not overwrite them. ...

Labels

You can also set Labels with instance template. Similar to Annotations, Labels in instance templates follow the same overriding logic applied to existing labels. ...note KubeBlocks adds system Labels, and do not overwrite them. ...

Image

The Image field in the instance template is used to override the Image field of the first container in the default template.

...note: Image field should be used with caution: for statefulset like databases, changing the Image often involves compatibility issues with data formats. When changing this field, please ensure that the image version in the instance template is fully compatible with that in the default template. ...

With KubeBlocks version 0.9 and above, detailed design for image versions is provided through ComponentVersion. It is recommended to manage versions using ComponentVersion.

NodeName

NodeName in the instance template overrides the same field in the default template.

NodeSelector

NodeSelector in the instance template overrides the same field in the default template.

Tolerations

Tolerations in the instance template overrides the same field in the default template.

If the Toleration in the instance template is identical to a Toleration in the default template (with the same Key, Operator, Value, Effect, and TolerationSeconds), then that Toleration will be ignored. Otherwise, it will be added to the list of Tolerations in the default template.

RuntimeClassName

RuntimeClassName in the instance template overrides the same field in the default template.

Resources

Resources in the instance template overrides the same field in the default template and gets the highest priority.

Env

The environment variables (Env) defined in the instance template will override any other environment variables except for the default Env set by KubeBlocks. The overriding logic is similar to Annotations and Labels. If an environment variable name is the same, the value or value source from the instance template will be used; if it's different, it will be added as a new environment variable.

Volumes

Used to override the Volumes field of the first container in the default template. The overriding logic is similar to Env, if the Volume Name is the same, the VolumeSource from the instance template will be used; otherwise, it will be added as a new Volume.

VolumeMounts

Used to override the VolumeMounts field of the first container in the default template. The overriding logic is similar to Volumes, meaning if the VolumeMount Name is the same, the MountPath and other values from the instance template will be used; otherwise, it will be added as a new VolumeMount.

VolumeClaimTemplates

Used to override the VolumeClaimTemplates generated by ClusterComponentVolumeClaimTemplate within the Component. The overriding logic is similar to Volumes, meaning if the PersistentVolumeClaim Name is the same, the PersistentVolumeClaimSpec values from the instance template will be used; otherwise, it will be added as a new PersistentVolumeClaim.