A Dedicated Host (DDH) is a single-tenant physical server that is running on the Alibaba Cloud virtualization platform. This topic describes the features of DDH.

Automatic deployment

The automatic deployment feature can help you select a dedicated host to deploy ECS instances. After a dedicated host is set to allow automatic deployment, it resides in the resource pool for automatic deployment under your account. You do not need to specify a dedicated host when you create an ECS instance. The system automatically selects a dedicated host from the resource pool to deploy the ECS instance. For more information about how to enable automatic deployment, see Set the dedicated host to enable automatic deployment.

The following table describes the application scenarios for automatic deployment.
Scenario Operation Result Reference
Create an ECS instance Specify a dedicated host. The ECS instance is deployed on the specified dedicated host.
Select Automatic Deployment ECS instances are automatically deployed.
Migrate an ECS instance from a shared host to a dedicated host. Specify a dedicated host. The ECS instance is deployed on the specified dedicated host.
Do not specify a dedicated host. ECS instances are automatically deployed.
Migrate ECS instances between different dedicated hosts Specify a dedicated host. The ECS instance is deployed on the specified dedicated host.
Do not specify a dedicated host. ECS instances are automatically deployed.
Note If the dedicated host where the ECS instance is located allows automatic deployment and has the most available resources, the ECS instance is still placed on the current dedicated host.

Host association

Host association is applicable to ECS instances that have enabled the No fees for stopped instances feature. You can specify whether an instance is placed on the original dedicated host when the instance is stopped and restarted. After the host is associated, you can make sure that the instance runs on the same physical server when it is restarted even through planned interruptions. This feature also helps you maintain the same deployment policy for the ECS instance.

The following table describes how to use the host association feature.
Scenario Operation Result
An ECS instance has enabled the No fees for stopped instances feature, and the instance is started again after it is stopped. Enable the host association feature

For more information, see Associate an ECS instance with a dedicated host.

The ECS instance is still deployed on the original dedicated host. If the available resources of the original dedicated host are insufficient, the instance fails to be restarted.
Disable host association

You can set Associate with DDH to No to disable this feature. For more information, see Associate an ECS instance with a dedicated host.

The ECS instance is first deployed on the original dedicated host. However, if the available resources of the original dedicated host are insufficient, the system automatically deploys the ECS instance on another dedicated host.

Resource efficiency

If the No fees for stopped instances feature is enabled, the CPU and memory resources used by the instance are released when you stop an instance.

For more information about how the instance is deployed when the instance is restarted, see Host association.

Upgrade and downgrade ECS instances

ECS instances created on a dedicated host support configuration changes. You can meet ever-changing workload requirements by upgrading or downgrading the instance type and adjusting the Internet bandwidth of the instance. For more information, see Upgrade or downgrade a subscription ECS instance.