Container Service for Kubernetes:Spread Elastic Container Instance-based pods across zones and configure affinities

Table of contents

• Prerequisites

• Precautions

• Terms

• Spread Elastic Container Instance-based pods across zones and configure affinities

  • Example 1: Use topology spread constraints to spread Elastic Container Instance-based pods across zones

  • Example 2: Configure pod affinities and node affinities to deploy pods in specific zones

• Strict Elastic Container Instance-based pod topology spread

Precautions

• When you spread Elastic Container Instance-based pods across zones, you can set the topologyKey parameter only to topology.kubernetes.io/zone.

• When you spread Elastic Container Instance-based pods across zones, you cannot add annotations to specify the priorities of the vSwitches to which pods are spread. If you have specified the priorities of vSwitches to which a pod can be spread, the pod cannot be spread across zones.

• You cannot spread Elastic Container Instance-based pods across zones in FastFailed mode. If the FastFailed mode is enabled for a pod, the pod cannot be spread across zones.

Terms

• For more information about pod topology spread and affinities, see Pod Topology Spread Constraints and Assigning Pods to Nodes.

• NodeAffinity

• PodAffinity

• maxSkew

Spread Elastic Container Instance-based pods across zones and configure affinities

The following examples show how to spread Elastic Container Instance-based pods across zones and configure affinities in an ACK Pro cluster that runs Kubernetes 1.22.

Example 1: Use topology spread constraints to spread Elastic Container Instance-based pods across zones

1. Add a topology spread constraint to the configuration of a workload.

   Perform the following steps to specify a topology spread constraint in the Spec parameter in the configuration of a pod or the Spec parameter in the configuration of a workload, such as a Deployment or Job.

     topologySpreadConstraints:
       - maxSkew: <integer>
         minDomains: <integer> # This parameter is optional and is in the Beta phase in Kubernetes 1.25 and later. 
         topologyKey: <string>
         whenUnsatisfiable: <string>
         labelSelector: <object>
         matchLabelKeys: <list> # This parameter is optional and is in the Beta phase in Kubernetes 1.27 and later. 
         nodeAffinityPolicy: [Honor|Ignore] # This parameter is optional and is in the Beta phase in Kubernetes 1.26 and later. 
         nodeTaintsPolicy: [Honor|Ignore] # This parameter is optional and is in the Beta phase in Kubernetes 1.26 and later.

   In this example, a Deployment whose pods are evenly distributed to multiple zones is created. The following code block shows the YAML template of the Deployment:

   Show YAML content

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: with-pod-topology-spread
     labels:
       app: with-pod-topology-spread
   spec:
     replicas: 10
     selector:
       matchLabels:
         app: with-pod-topology-spread
     template:
       metadata:
         labels:
           app: with-pod-topology-spread
       spec:
         affinity:
           nodeAffinity:
             preferredDuringSchedulingIgnoredDuringExecution:
             - weight: 1
               preference:
                 matchExpressions:
                 - key: type
                   operator: NotIn
                   values:
                   - virtual-kubelet
         topologySpreadConstraints:
           - maxSkew: 1
             topologyKey: topology.kubernetes.io/zone
             whenUnsatisfiable: DoNotSchedule
             labelSelector:
               matchLabels:
                 app: with-pod-topology-spread
         tolerations:
           - key: "virtual-kubelet.io/provider"
             operator: "Exists"
             effect: "NoSchedule"
         containers:
         - name: with-pod-topology-spread
           image: registry.k8s.io/pause:2.0
           resources:
             requests:
               cpu: "1"
               memory: "256Mi"

   Parameter	Description
   preferredDuringSchedulingIgnoredDuringExecution: - weight: 1 preference: matchExpressions: - key: type operator: NotIn values: - virtual-kubelet	The configuration specifies that the pods are preferentially scheduled to ECS nodes. For more information about the parameters, see Node affinity.
   topologySpreadConstraints: - maxSkew: 1 topologyKey: topology.kubernetes.io/zone whenUnsatisfiable: DoNotSchedule labelSelector: matchLabels: app: with-pod-topology-spread	The configuration specifies that the pods are evenly deployed across multiple zones. For more information about the parameters, see topologySpreadConstraints field.
   tolerations: - key: "virtual-kubelet.io/provider" operator: "Exists" effect: "NoSchedule"	kube-scheduler tolerates the taint of virtual nodes to schedule pods to the virtual nodes. For more information about the parameters, see Taints and Tolerations.

   Note

   If you want to schedule pods to ARM-based virtual nodes, you must add a toleration to the pods to tolerate the taint of the ARM-based virtual nodes.

2. Create a workload.

   Create a file named deployment.yaml and copy the preceding YAML template to the file. Then, run the following command to create a Deployment in the cluster:

   kubectl apply -f deployment.yaml

3. Verify the scheduling result of the workload.

   • Run the following command to query the nodes on which the Deployment deploys the pods:

     kubectl get po -lapp=with-pod-topology-spread -ocustom-columns=NAME:.metadata.name,NODE:.spec.nodeName --no-headers | grep -v "<none>"

   • Run the following command to query the number of pods that are created by the Deployment in each zone:

     kubectl get po -lapp=with-pod-topology-spread -ocustom-columns=NODE:.spec.nodeName --no-headers | grep -v "<none>" | xargs -I {} kubectl get no {} -ojson | jq '.metadata.labels["topology.kubernetes.io/zone"]' | sort | uniq -c

Example 2: Configure pod affinities and node affinities to deploy pods in specific zones

1. Add affinities to the configuration of a workload.

   In this example, a Deployment whose pods are deployed in a single zone is created. The following code block shows the YAML template of the Deployment:

   Show YAML content

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: with-affinity
     labels:
       app: with-affinity
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: with-affinity
     template:
       metadata:
         labels:
           app: with-affinity
       spec:
         affinity:
           podAffinity:
             requiredDuringSchedulingIgnoredDuringExecution:
             - labelSelector:
                 matchExpressions:
                 - key: app
                   operator: In
                   values:
                   - with-affinity
               topologyKey: topology.kubernetes.io/zone
           nodeAffinity:
             preferredDuringSchedulingIgnoredDuringExecution:
             - weight: 1
               preference:
                 matchExpressions:
                 - key: type
                   operator: NotIn
                   values:
                   - virtual-kubelet
         tolerations:
           - key: "virtual-kubelet.io/provider"
             operator: "Exists"
             effect: "NoSchedule"
         containers:
         - name: with-affinity
           image: registry.k8s.io/pause:2.0

   Parameter	Description
   podAffinity: requiredDuringSchedulingIgnoredDuringExecution: - labelSelector: matchExpressions: - key: app operator: In values: - with-affinity topologyKey: topology.kubernetes.io/zone	The configuration specifies that all the pods are deployed in a single zone. For more information about the parameters, see Node affinity.
   nodeAffinity: preferredDuringSchedulingIgnoredDuringExecution: - weight: 1 preference: matchExpressions: - key: type operator: NotIn values: - virtual-kubelet	The configuration specifies that the pods are preferentially scheduled to ECS nodes. For more information about the parameters, see Node affinity.
   tolerations: - key: "virtual-kubelet.io/provider" operator: "Exists" effect: "NoSchedule"	kube-scheduler tolerates the taint of virtual nodes to schedule pods to the virtual nodes. For more information about the parameters, see Taints and Tolerations.

   If you want to deploy the pods in a specific zone, delete the podAffinity parameter and add the following constraint to the nodeAffinity parameter: The following configuration specifies that the pods must be deployed in Beijing Zone A.

   requiredDuringSchedulingIgnoredDuringExecution:
     nodeSelectorTerms:
     - matchExpressions:
       - key: topology.kubernetes.io/zone
         operator: In
         values:
         - cn-beijing-a

2. Create a workload.

   Create a file named deployment.yaml and copy the preceding YAML template to the file. Then, run the following command to create a Deployment in the cluster:

   kubectl apply -f deployment.yaml

3. Verify the scheduling result of the workload.

   • Run the following command to query the nodes on which the Deployment deploys the pods:

     kubectl get po -lapp=with-affinity -ocustom-columns=NAME:.metadata.name,NODE:.spec.nodeName --no-headers | grep -v "<none>"

   • Run the following command to query the number of pods that are created by the Deployment in each zone:

     kubectl get po -lapp=with-affinity -ocustom-columns=NODE:.spec.nodeName --no-headers | grep -v "<none>" | xargs -I {} kubectl get no {} -ojson | jq '.metadata.labels["topology.kubernetes.io/zone"]' | sort | uniq -c

Strict Elastic Container Instance-based pod topology spread

By default, if you force the system to spread Elastic Container Instance-based pods across zones, kube-scheduler evenly deploys the pods of a workload across all zones. However, Elastic Container Instance-based pods may fail to be created in some zones. The following figure shows the scheduling result when the maxSkew parameter is set to 1. For more information about maxSkew, see maxSkew.

If the Elastic Container Instance-based pods in Zone B and Zone C fail to be created, two Elastic Container Instance-based pods will run in Zone A, whereas no Elastic Container Instance-based pod runs in Zone B or Zone C. This violates the constraint specified by the maxSkew parameter.

In an ACK Pro cluster, you can enable strict Elastic Container Instance-based pod topology spread to ensure that pods are strictly spread across zones. After you enable strict Elastic Container Instance-based pod topology spread, kube-scheduler first schedules a pod to each of Zone A, Zone B, and Zone C. kube-scheduler does not schedule pending pods until the scheduled pods are successfully created, as shown in the following figure.

Even if Pod A1 is successfully created, pending pods are not scheduled. This is because if the pod in Zone B or Zone C fails to be created, the constraint specified by the maxSkew parameter is violated. After Pod B1 is successfully created, kube-scheduler schedules a pod to Zone C. The following figure shows the scheduling result. Pods with orange shading are successfully created.

If you want to disable strict Elastic Container Instance-based pod topology spread, set the whenUnsatisfiable parameter to ScheduleAnyway. For more information, see Spread constraint definition.