Overview of a Migration Operation

The Logical Domains Manager on the source machine accepts the request to migrate a domain and establishes a secure network connection with the Logical Domains Manager running on the target machine. Once this connection has been established, the migration occurs. The migration itself can be broken down into different phases.

Phase 1: After connecting with the Logical Domains Manager running in the target host, information about the source machine and domain are transferred to the target host. This information is used to perform a series of checks to determine whether a migration is possible. The checks differ depending on the state of the source domain. For example, if the source domain is active, a different set of checks are performed than if the domain is bound or inactive.

Phase 2: When all checks in Phase 1 have passed, the source and target machines prepare for the migration. In the case where the source domain is active, this includes shrinking the number of CPUs to one and suspending the domain. On the target machine, a domain is created to receive the source domain.

Phase 3: For an active domain, the next phase is to transfer all the runtime state information for the domain to the target. This information is retrieved from the hypervisor. On the target, the state information is installed in the hypervisor.

Phase 4: Handoff. After all state information is transferred, the handoff occurs when the target domain resumes execution (if the source was active) and the source domain is destroyed. From this point on, the target domain is the sole version of the domain running.