Node Templates

What is it?

Node Templates are part of the Autoscaler component. They allow you to define virtual buckets of constraints such as:

• instance types to be used;
• lifecycle of the nodes to add;
• node provisioning configurations;
• and other various properties.

CAST AI will respect all the above settings when creating nodes for your workloads to run on.

UI is available at CAST AI console and you can find it in: Cluster --> Autoscaler --> Node Templates

Feature availability

Main attributes

Create a Node Template

• You have the following options to create node templates:

  • Create Node Template through the API
  • Create Node Template through the UI ( Cluster --> Autoscaler --> Node Templates )
  • Terraform

• Sometimes, when you create a Node Template, you may want to associate it with custom node configurations to be used when provisioning nodes. You can achieve this by linking the template with Node configuration

Using the shouldTaint flag

While creating a Node Template, you can choose if the nodes created by the CAST AI Autoscaler should be tainted or not. This is controlled through shouldTaint property in the API payload.

🚧

When shouldTaint is set to false

Since no taints will be applied on the nodes created by CAST AI, any pods being deployed to the cluster, even the ones without nodeSelector, might get scheduled on these nodes. This effect might not always be desirable.

When shouldTaint is set to true

apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  nodeSelector:
    scheduling.cast.ai/node-template: memory-optimized
  tolerations:
    - key: scheduling.cast.ai/node-template
      value: memory-optimized
      operator: Equal
      effect: NoSchedule
  containers:
    - name: busybox
      image: busybox:1.28
      args:
        - sleep
        - "1200"

When shouldTaint is set to false

apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  nodeSelector:
    scheduling.cast.ai/node-template: memory-optimized
  containers:
    - name: busybox
      image: busybox:1.28
      args:
        - sleep
        - "1200"

Using nodeSelector

You can use nodeSelector to schedule pods on the nodes created using the template. By default, you construct nodeSelector using the template name. However, you may choose to use a custom label to fit your use case better.

Using a node template name in nodeSelector

apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  nodeSelector:
    scheduling.cast.ai/node-template: memory-optimized
  containers:
    - name: busybox
      image: busybox:1.28
      args:
        - sleep
        - "1200"

Using multiple custom labels in nodeSelector

In case you have a node template with multiple custom labels custom-label-key-1=custom-label-value-1 and custom-label-key-2=custom-label-value-2. You can schedule your pods on a node created using that node template by providing nodeSelector with all the custom labels as described below:

apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  nodeSelector:
    custom-label-key-1: custom-label-value-1
    custom-label-key-2: custom-label-value-2
  containers:
    - name: busybox
      image: busybox:1.28
      args:
        - sleep
        - "1200"

Using nodeAffinity

You can use nodeAffinity to schedule pods on the nodes created using the template. By default, you construct nodeAffinity using the template name. However, you may choose to use a custom label to fit your use case better. The only supported nodeAffinity operator is In.

Using the node template name in nodeAffinity

apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
          - matchExpressions:
            - key: scheduling.cast.ai/node-template
              operator: In
              values:
                - "memory-optimized"
  containers:
    - name: busybox
      image: busybox:1.28
      args:
        - sleep
        - "1200"

Using a node template's custom labels in nodeAffinity

In case you have a node template with multiple custom labels custom-label-key-1=custom-label-value-1 and custom-label-key-2=custom-label-value-2. You can schedule your pods on a node created using that node template by providing nodeAffinity with all the custom labels as described below:

apiVersion: v1
kind: Pod
metadata:
  name: busybox-sleep
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
          - matchExpressions:
            - key: custom-label-key-1
              operator: In
              values:
                - "custom-label-value-1"
            - key: custom-label-key-2
              operator: In
              values:
                - "custom-label-value-2"
  containers:
    - name: busybox
      image: busybox:1.28
      args:
        - sleep
        - "1200"