Container Service for Kubernetes:Use ImageCache to accelerate the creation of elastic container instances

Introduction to ImageCache

An ImageCache represents a resource type defined by Elastic Container Instance, with each ImageCache corresponding to an image cache. Before you run containers, the elastic container instance must pull the specified images. Pulling large images over an unstable network can significantly delay the startup time of an elastic container instance. To mitigate this, Elastic Container Instance offers the image cache feature. You can create a cache snapshot from an image and then use the cache snapshot to create an elastic container instance. This eliminates or reduces the need to download image layers and therefore accelerates the creation of elastic container instances. For more information, see Overview of image caches.

By default, ACK Serverless clusters are deployed with the ImageCache CRD. Run the command kubectl get crd/imagecaches.eci.alibabacloud.com to confirm if the cluster supports ImageCache.

• If information about imagecaches.eci.alibabacloud.com is returned, the cluster supports ImageCache.

• If an error message is returned, it indicates that the cluster does not support ImageCache. To resolve this, update the ACK Virtual Node component to the latest version.

Billing

Fees for associated resources may apply during the creation and use of ImageCache. For more information, see Image caches billing.

Create an ImageCache

You can use one of the following methods to create an ImageCache:

Use an ImageCache

An ImageCache is a cluster-level resource that you can use to accelerate the creation of pods in different namespaces. When you create a pod by using an ImageCache, take note of the following items:

• Specify an image in the image cache for containers in the pod to improve the match degree.

• Set the image pulling policy (ImagePullPolicy) of containers in the pod to IfNotPresent to prevent repeated downloads of image layers.

When you create a pod from an ImageCache, you can add annotations to the metadata in the pod configuration file to enable automatic match of ImageCache or specify the ImageCache that you want to use. The following list describes the annotations:

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-auto-imc: "true"   # Enables automatic match of image caches
        k8s.aliyun.com/imc-perfect-match: "true"  # Specifies that all container images in the pod must match the image cache.
    spec:
      containers:
      - name: nginx
        image: registry.cn-shanghai.aliyuncs.com/eci_open/nginx:1.14.2
        ports:
        - containerPort: 80
        imagePullPolicy: IfNotPresent
      - name: busybox
        image: registry.cn-shanghai.aliyuncs.com/eci_open/busybox:1.30
        command: ["sleep"]
        args: ["999999"]
        imagePullPolicy: IfNotPresent

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-imc-id: imc-2ze5tm5gehgtiiga****  # Specifies an image cache.
    spec:
      containers:
      - name: nginx
        image: registry.cn-shanghai.aliyuncs.com/eci_open/nginx:1.14.2
        ports:
        - containerPort: 80
        imagePullPolicy: IfNotPresent