Elastic Container Instance:Overview of image caches

Feature description

Before you run containers, Elastic Container Instance must pull the specified images. Pulling large images over an unstable network requires an extended period of time when elastic container instances start. To accelerate the creation of elastic container instances, Elastic Container Instance provides the image cache feature. You can create a snapshot based on an image and then use the snapshot to create elastic container instances. This prevents or minimizes the downloads of images layers and accelerates the creation of instances.

For example, if you create an elastic container instance based on a Flink image that is approximately 386.26 MB in size on Docker Hub, preparing the image requires 50 seconds. If you use an image cache, preparing the image does not consume time. This significantly reduces the time that is required for starting the instance.

Methods to create an image cache

An image cache can be manually or automatically created.

Manually create an image cache

You can configure parameters such as the name and size of the image cache based on your business requirements. The following figure shows how to manually create an image cache.

• Each time an image cache is created, a snapshot is also created. You must manage manually created image caches.

• When you manually create an image cache, the system automatically creates a temporary elastic container instance and attaches a temporary performance level-1 (PL1) Enterprise SSD (ESSD) to the temporary instance. The temporary instance provides 2 vCPUs and 4 GiB of memory. The temporary instance pulls specified images to store in the ESSD. Then, the system creates a snapshot of the ESSD. After the image cache is created, the temporary instance and ESSD are automatically released.

• The instant image cache feature reduces the amount of time required to create an image cache. After you enable this feature, the system enables the instant access feature to create a temporary local snapshot. Then, you can use the local snapshot to create elastic container instances.

  Note

  After the local snapshot is created, the system begins to create a standard snapshot. During the creation of the standard snapshot, you can use the local snapshot to create elastic container instances. After the standard snapshot is created, the system removes the local snapshot. This way, you can use the standard snapshot to create elastic container instances.

• You can use the image cache reuse feature to accelerate the creation of the image cache. If you enable this feature, the system can automatically match existing image caches when you create an image cache. Duplicate image layers in existing image caches are reused to accelerate the creation of the image cache.

Automatically create an image cache

When you create an elastic container instance, you can enable automatic match of image caches. If no image cache is matched, the system creates a matched image cache during the instance creation. The following figure shows how to automatically create an image cache.

• A snapshot is created each time an image cache is created. Automatically created image caches are managed by Alibaba Cloud.

• During the creation of the image cache, the system creates a temporary elastic container instance. The temporary instance pulls specified images to store in the temporary storage space of the instance. Then, the system creates a snapshot of the temporary storage space. After the image cache is created, the temporary instance is automatically released.

  Note

  By default, each elastic container instance is assigned a temporary storage space of 30 GiB. If the image that you specify exceeds 30 GiB in size, adjust the size of the temporary storage space.

Comparison

The following table describes the comparison between manually and automatically created image caches.

Methods to use an image cache

You can use the image cache feature to accelerate the creation of an elastic container instance. If you want to use the image cache feature to create an elastic container instance, you can configure automatic match of image caches or specify an image cache to create the instance.

Precautions

• A single image cache can contain up to 20 images.

• To create an image cache, you need to pull container images. Therefore, the creation period of the image cache depends on factors such as the number of the images to be pulled, the size of the image used to create the image cache, and network conditions.

• When you manually create an image cache, the container image that you specify is used. When the system automatically creates an image cache, the container image that you declare in the elastic container instance is used.

  • If you select a private image, which is not hosted in Alibaba Cloud Container Registry, you must provide the access credentials including the IP address, username, and password of the repository to which the private image belongs.

  • If the selected image, such as a Docker image, needs to be pulled over the Internet, you must configure an elastic IP address (EIP) or a NAT gateway for the elastic container instance. For more information, see Enable Internet access for elastic container instances.

  • If the image cannot be pulled due to some reasons such as a timeout error of the remote repository, we recommend that you use ACR to upload the image to an Alibaba Cloud image repository.

• For manually created image caches, we recommend that you configure the retention period when you create the image caches to avoid unnecessary snapshot fees. For automatically created image caches, Alibaba Cloud manages the snapshots. You do not need to care for the retention period of the snapshots.

• After an image cache is created, you can learn about the creation process of the image cache through the creation events of the image cache. The system can retain up to 50 latest creation events.

Billing

For more information, see Image caches.