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

Automatic deployment

The automatic deployment feature allows you to select a dedicated host to deploy Elastic Compute Service (ECS) instances. After you enable automatic deployment for a dedicated host, the dedicated host resides in the resource pool of your Alibaba Cloud account for automatic deployment. When you create an ECS instance, you do not need to specify a dedicated host. The system selects a dedicated host from the resource pool to deploy the instance. For more information, see Set the dedicated host to enable automatic deployment.

The following table describes the use scenarios of automatic deployment.
Scenario Operation Result References
Create an ECS instance Specify a dedicated host The ECS instance is deployed on the dedicated host.
Select Allow Automatic Deployment The ECS instance is 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 dedicated host.
Specify no dedicated host The ECS instance is automatically deployed.
Migrate an ECS instance between two dedicated hosts Specify a dedicated host The ECS instance is deployed on the dedicated host.
Specify no dedicated host The ECS instance is automatically deployed.
Note If the dedicated host where the ECS instance resides allows automatic deployment and has the most available resources, the instance is still deployed on the dedicated host.

Host association

Host association is suitable for ECS instances that have enabled the economical mode. After an instance is associated with a dedicated host, the instance is still deployed on the dedicated host after it is stopped or restarted. Even if the instance enters the Stopped state, it is deployed on the original physical server. The feature also helps you maintain the same deployment method for ECS instances.

The following table describes the use scenarios of host association.
Scenario Operation Result
Stop and restart an ECS instance that has enabled the economical mode 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 dedicated host has no sufficient available resources, the instance fails to be restarted.
Disable the host association feature.

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

ECS first attempts to deploy the ECS instance on the original dedicated host. If the dedicated host has no sufficient available resources, ECS deploys the instance on another dedicated host.

Resource efficiency

If an ECS instance has enabled the economical mode, the CPU and memory resources that are used by the instance are released after the instance is stopped.

For more information, see Host association.

Instance upgrade and downgrade

If an ECS instance is created on a dedicated host, you can change the configurations of the instance. You can upgrade or downgrade the instance type, and adjust the public bandwidth of the instance based on your business requirements. For more information, see Upgrade or downgrade a subscription ECS instance.