Container Service for Kubernetes:Auto scaling for cross-zone deployment

Solution

To meet the requirement of auto scaling for cross-zone deployment, ACK provides the ack-autoscaling-placeholder component. The component fixes this issue by using resource redundancy. The component can scale out node pools in different zones concurrently instead of creating nodes in specific zones. For more information, see Use ack-autoscaling-placeholder to scale pods within seconds.

The following figure shows how to create nodes in two zones concurrently based on the existing architecture.

1. Use ack-autoscaling-placeholder as the bridge between the application pods and the node auto scaling component and create a placeholder pod in each zone. The priority of the placeholder pods must be lower than the priority of the application pods.

2. After the state of the application pods changes to Pending, the application pods replace the placeholder pods and are scheduled to the existing nodes of each zone. The state of the placeholder pods changes to Pending.

3. The placeholder pods are scheduled by using the nodeSelector. The node auto scaling component must create nodes in each zone to host the placeholder pods.

Step 1: Create a node pool for each zone and configure a custom node label

1. Log on to the ACK console. In the left-side navigation pane, click Clusters.

2. On the Clusters page, find the cluster that you want to manage and click the name of the cluster. On the details page of the cluster, choose Nodes > Node Pools in the left-side navigation pane.

3. In the upper-right corner of the Node Pools page, click Create Node Pool.

4. In the Create Node Pool dialog box, configure the parameters for the node pool. In this example, the auto-zone-I node pool for which the auto scaling feature is enabled is created in Zone I.

   The following table describes the key parameters. For more information about other parameters, see Create a node pool.

   Parameter	Description
   Node Pool Name	auto-zone-I
   vSwitch	Select a vSwitch deployed in Zone I.
   Auto Scaling	Enable auto scaling.
   Node Label	Set the Key parameter of the node label to avaliable_zone and the Value parameter to i.

5. Click Confirm Order.

   On the Node Pools page, you can find the node pools that you create. After the state of the auto-zone-I node pool changes to Active, the node pool is created.

6. Repeat the preceding steps to create a node pool with the auto scaling feature enabled for each zone that requires auto scaling.

Step 2: Deploy ack-autoscaling-placeholder and placeholder Deployments

1. In the left-side navigation pane of the ACK console, choose Marketplace > Marketplace.

2. On the App Catalog tab, find and click ack-autoscaling-placeholder.

3. On the ack-autoscaling-placeholder page, click Deploy.

4. In the Basic Information step, select a cluster from the Cluster drop-down list and a namespace from the Namespace drop-down list, and then click Next. Select a chart version from the Chart Version drop-down list, configure the parameters, and then click OK.

   After ack-autoscaling-placeholder is deployed, go to the cluster details page. In the left-side navigation, choose Applications > Helm. You can find that the application is in the Deployed state.

5. In the left-side navigation pane of the details page, choose Applications > Helm.

6. On the Helm page, find ack-autoscaling-placeholder-default and click Update in the Actions column.

7. In the Update Release panel, modify the YAML template based on your requirements and click OK. Deploy a placeholder Deployment in each zone.

   The following YAML template provides an example on how to deploy a placeholder Deployment in Zone I, Zone K, and Zone H:

   deployments:
   - affinity: {}
     annotations: {}
     containers:
     - image: registry-vpc.cn-beijing.aliyuncs.com/acs/pause:3.1
       imagePullPolicy: IfNotPresent
       name: placeholder
       resources:
         requests:
           cpu: 3500m     # The CPU request of the placeholder Deployment. 
           memory: 6      # The memory request of the placeholder Deployment. 
     imagePullSecrets: {}
     labels: {}
     name: ack-place-holder-I             # The name of the placeholder Deployment. 
     nodeSelector: {"avaliable_zone":i}   # The zone label. The label must be the same as the label that you specified in Step 1 when you created the node pool. 
     replicaCount: 10                     # The number of pods that are created in each scale-out activity. 
     tolerations: []
   - affinity: {}
     annotations: {}
     containers:
     - image: registry-vpc.cn-beijing.aliyuncs.com/acs/pause:3.1
       imagePullPolicy: IfNotPresent
       name: placeholder
       resources:
         requests:
           cpu: 3500m    # The CPU request of the placeholder Deployment. 
           memory: 6     # The memory request of the placeholder Deployment. 
     imagePullSecrets: {}
     labels: {}
     name: ack-place-holder-K            # The name of the placeholder Deployment. 
     nodeSelector: {"avaliable_zone":k}  # The zone label. The label must be the same as the label that you specified in Step 1 when you created the node pool. 
     replicaCount: 10                    # The number of pods that are created in each scale-out activity. 
     tolerations: []
   - affinity: {}
     annotations: {}
     containers:
     - image: registry-vpc.cn-beijing.aliyuncs.com/acs/pause:3.1
       imagePullPolicy: IfNotPresent
       name: placeholder
       resources:
         requests:
           cpu: 3500m   # The CPU request of the placeholder Deployment. 
           memory: 6    # The memory request of the placeholder Deployment. 
     imagePullSecrets: {}
     labels: {}
     name: ack-place-holder-H           # The name of the placeholder Deployment. 
     nodeSelector: {"avaliable_zone":h} # The zone label. The label must be the same as the label that you specified in Step 1 when you created the node pool. 
     replicaCount: 10                   # The number of pods that are created in each scale-out activity. 
     tolerations: []
   fullnameOverride: ""
   nameOverride: ""
   podSecurityContext: {}
   priorityClassDefault:
     enabled: true
     name: default-priority-class
     value: -1

   After you update the YAML file, a placeholder Deployment is deployed in each zone.

Step 3: Create a PriorityClass for a workload

1. Create a file named priorityClass.yaml by using the following YAML template:

   apiVersion: scheduling.k8s.io/v1
   kind: PriorityClass
   metadata:
     name: high-priority
   value: 1000000              # Specify the priority value. The value must be higher than the default priority value of the Deployments that you create in Step 2. 
   globalDefault: false
   description: "This priority class should be used for XYZ service pods only."

   If you do not want to configure a PriorityClass for a workload, you can configure a global PriorityClass as the default configuration. After you deploy the configurations, application pods can automatically replace placeholder pods.

   apiVersion: scheduling.k8s.io/v1
   kind: PriorityClass
   metadata:
     name: global-high-priority
   value: 1                              # Specify the priority value. The value must be greater than the default priority of the Deployments that you create in Step 2. 
   globalDefault: true
   description: "This priority class should be used for XYZ service pods only."

2. Run the following command to deploy the PriorityClass for the workload:

   kubectl apply -f priorityClass.yaml

   Expected output:

   priorityclass.scheduling.k8s.io/high-priority created

Step 4: Deploy a workload

In this example, a workload is deployed in Zone I.

1. Create a file named workload.yaml by using the following YAML template:

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: placeholder-test
     labels:
       app: nginx
   spec:
     replicas: 1
     selector:
       matchLabels:
         app: nginx
     template:
       metadata:
         labels:
           app: nginx
       spec:
         nodeSelector:                        # Select a node to deploy the workload. 
           avaliable_zone: "i"
         priorityClassName: high-priority     # Specify the name of the PriorityClass that is created in Step 3. If you enable global configurations, this parameter is optional. 
         containers:
         - name: nginx
           image: nginx:1.7.9
           ports:
           - containerPort: 80
           resources:
             requests:
               cpu: 3                         # Specify the resource request of the workload. 
               memory: 5

2. Run the following command to deploy the workload:

   kubectl apply -f workload.yaml

   Expected output:

   deployment.apps/placeholder-test created

   Verify the result

   After you deploy the workload, go to the cluster details page and choose Workloads > Pods in the left-side navigation pane. On the Pods page, you can find that the PriorityClass of the workload has a higher priority value than that of the placeholder pods. This way, the workload pods can run on the nodes that are added. The placeholder pods trigger the node auto scaling component to create nodes in each zone concurrently and prepare for the next scale-out activity requested by the workload.

   Choose Nodes > Nodes. On the Nodes page, you can find that the workload pod runs on the node that hosts the placeholder pod.