Why and when do I need Virt-Who?

The virt-who agent is a specific tool that assists subscription services. This article focuses on what virt-who does and when you need virt-who.

BACKGROUND
Some RHEL subscriptions offer guest entitlements in addition to the physical entitlement provided in the base subscription. When a subscription offers guest entitlements, there is a contractual obligation for those guests to execute on the host where the guest entitlements are offered.

This strategy was finalized in the 2013 model subscriptions where the subscription tools provided by the RHSM suite were updated to become sensitive to the virt-limit (number of guest entitlements) and the "host-limiting" (flag requiring host/guest mapping [see below]) attributes of the subscription which support the contractual statements. Thus, the workflow under the RHSM tools requires the host/hypervisor to attach the physical entitlement before the guest entitlements can be used by the guests.

WHAT VIRT-WHO DOES
However, guests running on a hypervisor do not know what host they are running on (for the security of the hypervisor infrastructure). So, the subscription service cannot completely reconcile the guest subscription until the host/guest mapping is available.

The virt-who agent interrogates the hypervisor infrastructure and provides the host/guest mapping to the subscription service. Here’s how: the virt-who agent uses read-only commands to gather the host/guest associations for the subscription services. This way, the guest subscriptions offered by a subscription can be unlocked and available for the guests to use. Please see the diagram below.

WHEN YOU NEED VIRT-WHO
For both 2010 and 2013 models, guests were expected to consume only RHEL guest subscriptions offered by that specific host. To support this business rule, subscription services have been changing slowly, resulting in tooling differences between the entitlement system versions. Some customers may be confused as to where the virtual guests may be executed within the environment. To help explain the use/behavior and reduce confusion, please see this table:

REFERENCE DIAGRAM

Resources:

1. Documents and Articles

   1. Virt-Who Processes, Queries, and Data

For more KB articles/solutions related to Virt-who and Virtual Datacenter (VDC) Subscriptions Issues, please refer to the Consolidated Troubleshooting Article for Virt-who and Virtual Datacenter (VDC) Subscriptions Issues