Image overview - Elastic Compute Service - Alibaba Cloud Documentation Center

An ECS image is a template for creating ECS instances. It contains the operating system (OS) and pre-configured data required to launch and run an instance. You must select an image when you create an ECS instance. The image must be compatible with your chosen instance type and can include a system disk, or a combination of a system disk and data disks. You can use images provided by Alibaba Cloud or other developers, create your own custom image, or use an image shared with you by another user. This topic explains how to choose an image, describes the different types of images available, and provides guides for common tasks.

How to choose an image

When you choose an image to create an ECS instance, consider the following factors:

Deployment region
Choose your deployment region first to narrow the available image options. Images are specific to a region.
- Alibaba Cloud typically provides public images in all regions.
- The availability of Marketplace and community images depends on the regions where their publishers release them.
- Custom images are available in the region where you create or import them. You can also copy custom images to other regions.
Operating system
Select an OS based on your technology stack, team expertise, and compliance requirements. For more information, see Public images.
- Windows Server: Offers a user-friendly interface, ease of use, and broad software support. It is suitable for running Windows applications, enterprise web services, databases such as SQL Server, and file and print services.
- Linux and Unix distributions
  - Alibaba Cloud Linux: Developed by Alibaba Cloud and is compatible with the CentOS ecosystem.
  - Anolis OS: An open source operating system.
  - CentOS: An open source distribution of Red Hat Enterprise Linux (RHEL). CentOS is no longer maintained and is not recommended for new deployments.
  - Red Hat Enterprise Linux: An operating system developed by Red Hat for enterprise applications. It offers a comprehensive set of features and is a paid product.

Instance type compatibility

Images provide information about their system architecture (32-bit or 64-bit), memory requirements, and boot mode. Use this information to ensure the image is compatible with your selected instance type.

System architecture	Memory size	Instance requirements
32-bit	For memory under 4 GiB	Instance memory: 4 GiB or less. CPU cores: A maximum of 4 cores for 32-bit Windows operating systems.
64-bit	For memory of 4 GiB or more	Instance memory: More than 4 GiB.

For more information about image and instance type compatibility with boot modes, see Instance boot modes.

Special image requirements
For a clean operating system, use a public image from Alibaba Cloud. If your business requires a specially configured environment, or if you want to bundle your application with the OS, consider using a Marketplace image or building your own custom image.
Image costs
Creating an ECS instance from a paid commercial image or from a custom image that is based on a paid commercial image incurs licensing fees. For more information, see Image billing.

Image types

Alibaba Cloud's technical support varies by the image type used to create an instance.

Image type	Description	Technical support
Public images	Images that are provided and maintained by Alibaba Cloud. They are licensed and have passed rigorous security and stability tests. Public images include Windows Server and popular Linux distributions to help you quickly set up a basic environment.	For Alibaba Cloud Linux images, Alibaba Cloud provides full technical support for any issues you encounter while using the Alibaba Cloud Linux OS. For third-party commercial and open source operating systems, the support is as follows: For open source operating systems, contact the respective open source community for support. Alibaba Cloud may assist with the investigation. For commercial operating systems, Alibaba Cloud provides the license and works with the OS vendor to offer technical support.
Custom images	An image that you create from an existing instance or a snapshot. This is useful for deploying applications with specific configurations or for setting up a standardized environment.	Custom images created from public images receive the same support as the source public image. For imported images, the support is as follows: Alibaba Cloud does not provide technical support for imported open source operating systems. If you use a license provided by Alibaba Cloud for an imported commercial operating system, Alibaba Cloud works with the OS vendor to provide technical support.
Shared images	An image that another Alibaba Cloud account has shared with you. This is ideal for team collaboration.	Alibaba Cloud does not provide technical support for shared images. Contact the account owner who shared the image.
Marketplace images	Images provided by Alibaba Cloud or third-party independent software vendors (ISVs). These images often include pre-installed software and are suitable for deploying specific applications. Marketplace images are classified into the following types based on the provider: Images published by Alibaba Cloud. Images published by third-party ISVs through Alibaba Cloud Marketplace. All Marketplace images are tested for security and stability by their publishers.	For images published by Alibaba Cloud, the support is the same as for public images. For images published by ISVs, the ISV provides technical support.
Community images	An image that any Alibaba Cloud user has published for public use in the image community.	Alibaba Cloud does not provide technical support for community images.

Note

The technical support described above depends on the image's OS being within its support lifecycle. For operating systems that have reached their End of Life (EOL), a different support policy applies. For more information, see OS lifecycle overview.
Alibaba Cloud regularly updates public images with new features and security patches. For more information, see Public image release notes. When you select a public image on the ECS instance buy page, the latest version is selected by default. To use an older version, you can call the RunInstances API operation and specify the image ID.
Security is a shared responsibility between you and Alibaba Cloud. Alibaba Cloud is responsible for the security of the cloud platform itself, including its hardware, software, and networks. You are responsible for the security of your ECS instances. This includes managing the OS, such as applying updates and security patches, configuring any software you install, and managing the security group firewall rules. For more information, see ECS security.

Relationship between custom images, instances, and snapshots

An image is a template for creating and launching instances. An instance is a virtual machine created from an image and other configuration parameters. A snapshot is a point-in-time backup of an instance's disks.

Understanding the relationship between custom images, instances, and snapshots helps you use them more effectively. The following diagram shows how a snapshot serves as a data backup of an instance at a specific point in time. You can create a custom image from either an instance (ECS 1) or a snapshot. You can then use that custom image to launch another instance (ECS 2).

Custom images and snapshots can both be used for data backup, but they differ in their primary use cases and functionality.

Key differences

Item	Image	Snapshot
Definition	An image is a full backup of an ECS instance, including its configuration, OS, installed software, and data. For more information, see Back up and restore data by using images.	A snapshot is a point-in-time backup of a single cloud disk or a group of cloud disks (in a snapshot-consistent group). For more information, see Back up and restore data by using snapshots.
Use cases	Backing up systems that change infrequently, such as a fully configured application server. After you create a custom image from a configured ECS instance, you can use it to quickly launch new instances, which is ideal for batch deployments. Migrating systems and data. Restoring systems across zones or regions. For example, you can create an instance in a new zone from a custom image, or copy an image to another region and use it to create an instance there.	Performing regular backups of cloud disk data. You can set up automatic snapshot policies to create backups daily, weekly, or monthly. Creating temporary backups of cloud disk data. For example: Before making significant system changes like updates or application deployments, you can manually create a snapshot to ensure that you can roll back if something goes wrong. Before you resize a system disk. For migrating data between cloud disks. You can create a snapshot of one disk and use it as the data source for a new disk.
Functionality	Can be used to directly create new ECS instances. Always includes a backup of the system disk. It may also include data disk backups, depending on whether the source instance had data disks or whether data disks were included when the image was created from snapshots. Can be used to replace the system disk of the source instance or other instances, or to create new instances.	Cannot be used to directly create new ECS instances. Can be a backup of either a system disk or a data disk. Can be used to roll back the original cloud disk or create new cloud disks.

Other relationships

When you create a custom image:
- You can create a custom image from a system disk snapshot. For more information, see Create a custom image from a snapshot.
- When you create a custom image from an ECS instance, a snapshot of each cloud disk (both system and data disks) attached to the instance is automatically created. The resulting custom image is a collection of these snapshots. For more information, see Create a custom image from an instance.
When you delete custom images and snapshots:
- When you delete a custom image, you can choose to either delete or retain the associated snapshots. For more information, see Delete a custom image.
- Before you can delete a snapshot associated with an image, you must first delete the image. For more information, see Delete a snapshot.

Limitations

Restriction item	Limit	How to increase quota
Maximum custom images per account per region	Quota ID: `q_user-image-count`	View or increase ECS quotas
Maximum users a custom image can be shared with	Quota ID: `q_user-per-image-shared-user-count`	View or increase ECS quotas
Image and instance type compatibility	Instance types with 4 GiB or more of memory cannot use 32-bit images.	Not applicable

How-to guides

Find an image
To quickly find the right image among the many public, Marketplace, custom, and shared images for creating your ECS instance, see Find an image.

Use custom images

You can create custom images to suit your specific needs. For more information, see Overview of custom images. The following table describes basic operations that you can perform on custom images.

Operation	When to use	Reference
Create an image	Capture an instance's current state or a snapshot as an image. Preserves a known-good configuration for reuse.	Create a custom image from an instance and Create a custom image from a snapshot
Import an image	Import images from on-premises devices or other cloud providers to migrate to Alibaba Cloud.	Import an image
Update an image	Refresh an image's software and configuration with OOS.	Update a custom image
Copy an image	Deploy an image across regions, or change the encryption status of images within or across regions.	Copy a custom image
Share an image	Share an image with other Alibaba Cloud accounts so they can launch instances from it.	Share a custom image
Export an image	Export an image to an OSS bucket for backup or download to an on-premises device.	Export a custom image
Modify image information	Update the name, description, NVMe drive settings, or boot mode of an image.	Modify the attributes and tags of an image
Delete an image	Remove an unneeded image. Only the creator can delete it.	Delete a custom image

Use Image Builder
Image Builder provides a centralized service for customizing image content, performing maintenance and testing, and managing distribution and sharing across regions and accounts. In Image Builder, you define a template that specifies a source image, components, and other tasks to be performed during the build process. This process creates a new image based on your template.