Workload Affinity

Using the CCE Console

Workload affinity determines the pods as which the target workload will be deployed in the same topology domain.

1. Log in to the CCE console and choose Workloads > Deployments or Workloads > StatefulSets in the navigation pane.
2. Click a workload name in the Deployment or StatefulSet list. On the displayed workload details page, click the Scheduling Policies tab and then click Add Custom Scheduling Policy.
3. In the Pod Affinity area, set the namespace, topology key, and the label requirements to be met.

   There are two types of pod affinity rules: Required (hard rule) and Preferred (soft rule). The label operators include In, NotIn, Exists, and DoesNotExist.

   Table 1 Pod affinity settings

   Parameter	Description
   Required	It specifies a rule that must be met in scheduling. It corresponds to requiredDuringSchedulingIgnoredDuringExecution in Kubernetes. You can click Add Rule to add multiple required rules. Ensure that all the labels specified in the rules must be in the same workload. Each rule requires a namespace and topology key.
   Preferred	It specifies a preference in scheduling. It corresponds to preferredDuringSchedulingIgnoredDuringExecution in Kubernetes. You can click Add Rule to add multiple preferred rules. The scheduler will try to enforce the rules but will not guarantee. If the scheduler cannot satisfy any one of the rules, the pod will still be scheduled.

4. Set a rule according to the following table. You can click Add Selector to configure multiple selectors for a rule.

   Table 2 Selector settings

   Parameter	Description
   Weight	This parameter is unavailable for a required rule. Set the weight of a preferred rule. A higher weight indicates a higher priority.
   Namespace	By default, the namespace of the current pod is used. You can also use another namespace.
   Topology Key	Key of the worker node label that the system uses to denote a topology domain in which scheduling can be performed. Default and custom node labels can be used.
   Label	Label of the workload. You can customize the label name.
   Operator	The following relations are supported: In, NotIn, Exists, and DoesNotExist
   Value	Tag value. Operators In and NotIn allow one or more label values. Values are separated with colons (;). Operators Exists and DoesNotExist are used to determine whether a label exists, and do not require a label value.
   Operation	You can click Delete to delete a selector.
   Add Selector	A selector corresponds to matchExpressions in Kubernetes. You can click Add Selector to add multiple selectors for a scheduling rule. The rule is applied in scheduling only when all its selectors are satisfied.

   Figure 1 Pod affinity scheduling policy
   

Using kubectl

This section uses Nginx as an example to describe how to configure pod affinity.

Prerequisites

A workload that uses the nginx container image has been deployed on a node.

Procedure

Set Namespace to default and Topology Key to the built-in node label kubernetes.io/hostname, which means that the scheduling scope is a node. Set labels app and type and their value to redis and database, respectively. Set Operator to In and click OK.

The YAML of the workload with pod affinity is as follows:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  namespace: default
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx 
        imagePullPolicy: Always
        name: nginx
      imagePullSecrets:
      - name: default-secret
      affinity:
        nodeAffinity: {}
        podAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            - labelSelector:
                matchExpressions:
                  - key: app
                    operator: In
                    values:
                      - redis
                  - key: type
                    operator: In
                    values:
                      - database
              namespaces:
                - default
              topologyKey: kubernetes.io/hostname