tencent cloud

Image Cache Overview

This document describes how image cache works and its billing rules, creation, and usage method. You can use image cache to accelerate image pull during instance creation so as to expedite instance startup. This capability is applicable to EKS cluster Pods, supernodes, and container instances.

How It Works

When image cache accelerates instance startup, it will start a container instance in advance to pull the image, store the image in a data disk with a customizable size, and use the data disk as the cache of cloud disk snapshot, that is, the image data is already stored in the snapshot. You can choose to automatically or manually match the image cache when creating a container instance or Pod, and the specified number of data disks will be created based on the image snapshot and directly mounted to the instance to avoid image layer download, speeding up container instance and Pod creation.

Compared with the image reuse capability, image cache has the following strengths:

• It has no time limit and is only subject to the lifecycle of the image cache (snapshot).
• You only need to cold start a Pod in advance, which will be terminated immediately after snapshot creation.
• It has no limit on AZs, as AZs will be automatically matched during cloud disk creation based on snapshot.
• It has no limit on workloads, as workloads in the same region can be matched.

Billing

The following resources are involved when you create an image cache, and their billing rules are as detailed below:

When the image cache is used, a Premium Cloud Storage data disk with the same capacity will be created based on the matched image cache snapshot and bound to the Pod. Therefore, in addition to the Pod creation fees, data disk fees will also be incurred.

• Data disk fees = capacity * unit price * instance running duration

Directions

Creating image cache

1. Log in to the TKE console.
2. Select EKS > Image Cache on the left sidebar to enter the Image Cache page.
3. Click Create Instance and configure the relevant parameters.

• Instance Name: optional.
• Region: select as needed.
• Container network: assign an IP address within the container network IP range to the container instance.
• Security Group: a security group has the capabilities of a firewall and can limit the network communication of the instance. It is "default" by default.
• Image: select the image and version to be cached as needed.
• Image Credentials: when you select Docker Hub or a private image in a third-party image repository, you must enter the image credentials, i.e., access address, username, and password of the repository.
• Advanced configuration:
  • Bind EIP: you need to bind an EIP to access the public network when pulling an image from the internet.
  • Cache Size: it determines the size of the snapshot and the data disk bound during instance creation.
  • Expiration Policy: select the retention duration of the image cache, which is "Permanent" by default.

4. Click Create. After the image cache is created, it will be displayed in the image cache list. You can click the event name to view the creation progress.

Using image cache

When creating an EKS Pod or container instance, you can enable image cache in Advanced Configuration. There are two image cache match methods, which you can select as needed.

Using image cache on supernodes

You can specify a Pod annotation to use an image cache on supernodes. For more information, see EKS Annotation.

Automatically match:
eks.tke.cloud.tencent.com/use-image-cache: auto
Manually specify:
eks.tke.cloud.tencent.com/use-image-cache: imc-xxx

Match result

You can check whether the match succeeds in the instance creation event.

If the image cache is matched successfully, the following event will be displayed:

If this event is not displayed, no appropriate image caches have been matched.

Note that if you choose to manually match an image cache but it fails to be matched, an image will be pulled from the newly created data disk, and the following event will be displayed: