Virtual Guests and Hosts

When the CentOS Subscription Manager process checks the system facts, it attempts to identify whether the system is a physical machine or a virtual guest. The Subscription Manager can detect guests for several different virtualization services, including:

• KVM

• Xen
• HyperV
• VMWare ESX

Subscription Manager records a unique identifier called a guest ID as one of the system facts for a virtual guest. A special process, libvirt-rhsm, checks VMWare, KVM, and Xen processes and then relays that information to Subscription Manager and any configured subscription service (Certificate-based CentOS Network or a local Subscription Asset Manager). Each guest machine on a host is assigned a guest ID, and that guest ID is both associated with the host and used to generate the identity certificate for the guest when it is registered.

Some Community Enterprise Linux variants are specifically planned for virtual hosts and guests. The corresponding subscriptions are divided into a certain quantity of physical hosts and then a quantity of allowed guests. Community Enterprise Linux add-ons may even be inherited, so that when a host machine is subscribed to that entitlement, all of its guests are automatically included in that subscription. (CentOS layered products usually do not draw any distinction between virtual and physical systems; the same type of subscription is used for both.) If the system is a guest, then virtual entitlements are listed with the available subscriptions. If no more virtual entitlements are available, then the subscription service will apply physical entitlements.

Virtual and physical subscriptions are identified in the Type column.

Figure 14.12. Virtual and Physical Subscription

The distinction of being a physical machine versus virtual machine matters only in the priority of how entitlements are consumed. Virtual machines are recorded in the subscription service inventory as a regular system type of consumer.

Virtual guests are registered to the subscription service inventory as regular systems and subscribe to entitlements just like any other consumer.

Virtual entitlements can only be used by virtual machines. Physical entitlements can be used by both physical and virtual machines. When ascertaining what subscriptions are available for autosubscription, preference is given first to virtual entitlements (which are more restrictive in the type of consumer which can use them), and then to physical entitlements.