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How Amazon EC2 Dedicated Host works

Dedicated Hosts and the host resource groups recovery process use host-level health checks to assess Dedicated Host availability and to detect underlying system failures. The type of Dedicated Host failure determines if Dedicated Host auto recovery is possible. Examples of problems that can cause host-level health checks to fail include:

Dedicated Host auto recovery

When a system power or network connectivity failure is detected on your Dedicated Host, Dedicated Host auto recovery is initiated and Amazon EC2 automatically allocates a replacement Dedicated Host in the same Availability Zone as the original Dedicated Host. The replacement Dedicated Host receives a new host ID, but retains the same attributes as the original Dedicated Host, including:

When the replacement Dedicated Host is allocated, the instances are recovered on to the replacement Dedicated Host. The recovered instances retain the same attributes as the original instances, including:

Additionally, the built-in integration with Amazon License Manager automates the tracking and management of your licenses.

If instances have a host affinity relationship with the impaired Dedicated Host, the recovered instances establish host affinity with the replacement Dedicated Host.

When all of the instances have been recovered on to the replacement Dedicated Host, the impaired Dedicated Host is released, and the replacement Dedicated Host becomes available for use.

When host recovery is initiated, the Amazon account owner is notified by email and by an Amazon Health Dashboard event. A second notification is sent after the host recovery has been successfully completed.

If you are using Amazon License Manager to track your licenses, Amazon License Manager allocates new licenses for the replacement Dedicated Host based on the license configuration limits. If the license configuration has hard limits that will be breached as a result of the host recovery, the recovery process is not allowed and you are notified of the host recovery failure through an Amazon SNS notification (if notification settings have been configured for Amazon License Manager). If the license configuration has soft limits that will be breached as a result of the host recovery, the recovery is allowed to continue and you are notified of the limit breach through an Amazon SNS notification. For more information, see Using License Configurations and Settings in License Manager in the Amazon License Manager User Guide.

Host recovery states

When a Dedicated Host failure is detected, the impaired Dedicated Host enters the under-assessment state, and all of the instances enter the impaired state. You can't launch instances on to the impaired Dedicated Host while it is in the under-assessment state.

After the replacement Dedicated Host is allocated, it enters the pending state. It remains in this state until the host recovery process is complete. You can't launch instances on to the replacement Dedicated Host while it is in the pending state. Recovered instances on the replacement Dedicated Host remain in the impaired state during the recovery process.

After the host recovery is complete, the replacement Dedicated Host enters the available state, and the recovered instances return to the running state. You can launch instances on to the replacement Dedicated Host after it enters the available state. The original impaired Dedicated Host is permanently released and it enters the released-permanent-failure state.

If the impaired Dedicated Host has instances that do not support host recovery, such as instances with instance store-backed volumes, the Dedicated Host is not released. Instead, it is marked for retirement and enters the permanent-failure state.

Scenarios without Dedicated Host auto recovery

Dedicated Host auto recovery does not occur when the host is scheduled for retirement. You will receive a retirement notification in the Amazon Health Dashboard, an Amazon CloudWatch event, and the Amazon account owner email address receives a message regarding the Dedicated Host failure. Follow the remedial steps described in the retirement notification within the specified time period to manually recover the instances on the retiring host.

Stopped instances are not recovered on to the replacement Dedicated Host. If you attempt to start a stopped instance that targets the impaired Dedicated Host, the instance start fails. We recommend that you modify the stopped instance to either target a different Dedicated Host, or to launch on any available Dedicated Host with matching configurations and auto-placement enabled.

Instances with instance storage are not recovered on to the replacement Dedicated Host. As a remedial measure, the impaired Dedicated Host is marked for retirement and you receive a retirement notification after the host recovery is complete. Follow the remedial steps described in the retirement notification within the specified time period to manually recover the remaining instances on the impaired Dedicated Host.