Elastic Container Instance:Configure multiple zones to create a pod

Prerequisites

vSwitches are created in different zones of the virtual private cloud (VPC) where you want to create an elastic container instance.

• For information about how to create a vSwitch, see Create and manage a vSwitch.

• For information about the regions and zones where Elastic Container Instance is available, see Regions and zones.

Background information

When you create an elastic container instance, you can specify multiple zones by specifying multiple vSwitches. The system then distributes the requests across all the specified zones at random. If requested resources are insufficient within one zone, the system tries to create the instance in a different zone.

When you specify multiple zones (vSwitches), take note of the following items:

• The specified vSwitches must belong to the same VPC.

• You can specify up to 10 vSwitches.

You can specify multiple instance types across multiple zones to further improve the success rate of creating elastic container instances.

Configuration description

You can specify multiple zones for a cluster or a pod.

• If you want to specify multiple zones for a cluster, you need to specify multiple vSwitches for the cluster. The setting takes effect on all pods within the cluster.

• If you want to specify multiple zones for a pod, you need to specify multiple vSwitches when you create the pod. The setting takes effect only on the pod.

Specify multiple zones when you create a cluster

Before you create the cluster, we recommend that you create multiple vSwitches of different zones within the cluster VPC. When you create the cluster, you can select the VPC and then select multiple vSwitches to specify multiple zones. The following figure shows how to specify multiple vSwitches when you create a Container Service for Kubernetes (ACK) Serverless cluster in the ACK console.

Specify multiple zones for an existing cluster

The method of configuring multiple zones varies based on the version of the ack-virtual-node component that you use.

• If the version of your ack-virtual-node component is v2.0.0.90-15deb126e-aliyun or later, modify the eci-profile.

• If the version of your ack-virtual-node component is earlier than v2.0.0.90-15deb126e-aliyun, modify the value of the relevant environment variable.

Specify multiple zones when you create a pod

You can add the following annotations to the metadata in the configuration file of a pod to specify multiple zones:

• k8s.aliyun.com/eci-vswitch: the IDs of vSwitches that are used to specify multiple zones.

• k8s.aliyun.com/eci-schedule-strategy: the multi-zone scheduling policy. Valid values: VSwitchOrdered and VSwitchRandom. The following table describes the scheduling policies.

  Note

  If you do not specify the k8s.aliyun.com/eci-schedule-strategy annotation, the VSwitchRandom policy is used.

  Policy	Scheduling description
  VSwitchOrdered: The system tries to create the pod in the specified zone order.	If you want to mount a disk to the pod that you are creating, the zone of the disk must be the same as the zone of the pod. The zones that cannot provide both the pod and disk are filtered out. The system tries to create the pod in the specified order. If resources in the first zone are insufficient, the system tries the second zone, and so on, until the pod is created.
  VSwitchRandom: The system tries to create the pod in a random zone order.	If you want to mount a disk to the pod that you are creating, the zone of the disk must be the same as the zone of the pod. The zones that cannot provide both the pod and disk are filtered out. The system tries the specified vSwitches (corresponding to zones) in a random order. If you specified specifications for the pod that you are creating, zones that have a reserved instance for the specified pod specifications are preferentially used to create the pod. Zones that provide higher storage performance are preferentially used to create the pod. The following early zones are less preferentially used to create the pod: cn-beijing-e and cn-beijing-d cn-shenzhen-a, cn-shenzhen-b, and cn-shenzhen-c cn-hangzhou-b, cn-hangzhou-e, and cn-hangzhou-f cn-shanghai-a and cn-shanghai-c

Sample configurations:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: test
  labels:
    app: test
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      name: nginx-test
      labels:
        app: nginx
        alibabacloud.com/eci: "true" 
      annotations:
        k8s.aliyun.com/eci-vswitch: "vsw-bp1xpiowfm5vo8o3c****,vsw-bp1rkyjgr1xwoho6k****"    # Specifies multiple vSwitch IDs.
        k8s.aliyun.com/eci-schedule-strategy: "VSwitchOrdered"   # Configures a multi-zone scheduling policy.
    spec:
      containers:
      - name: nginx
        image: registry.cn-shanghai.aliyuncs.com/eci_open/nginx:1.14.2
        ports:
        - containerPort: 80

What to do next

If you use a network address translation (NAT) gateway to access the Internet and you configure multiple zones (vSwitches) to create elastic container instances, you must check whether the number of source network address translation (SNAT) entries that you configured for the NAT gateway is sufficient for the number of zones that you configured.

For example, when you create an SNAT entry, you specify a vSwitch for it. If you specify multiple vSwitches when you create an elastic container instance, you must increase SNAT entries for the new vSwitches to ensure that the elastic container instances that are connected to the new vSwitches can access the Internet.