Subscriptions define an element or attribute that it covers for that product. For a layered product such as Red Hat Directory Server, this may be a single instance of the application or server. The attribute could also be based on the physical characteristics of the system, such as a socket pair. Whatever the counted element is, is an instance.
Whatever the element is, there must be a subscription for every occurance of the element. For example, Red Hat Enterprise Linux subscriptions commonly cover a socket pair. If there are four sockets on a system, then the system requires two subscriptions — one for each socket pair.
Most subscriptions can be combined or stacked to cover each instance. There are some rules on what subscriptions can be combined:
Subscriptions can be combined by using multiple quantities from the same subscription set.
Subscriptions from different contracts can be combined together as long as they are compatible (e.g., for the same architecture and the same type of instance).
Only the same product subscription can be combined. RHEL Server for 2-Sockets can be stacked with another RHEL Server for 2-Sockets subscription, but not with RHEL Server for Virtualization, even if they both cover the socket count.
Only the subscriptions with the same service level can be stacked. For example, if the first subscription attached to a system has a premium service level, then it can only be stacked with other subscriptions with a premium service level.
To combine subscriptions in the Subscription Manager UI, simply set the Quantity field to the required quantity to cover the count.
Figure 4. Stacking Quantities
Example 5. Stacking in the Command Line
To combine subscriptions from the command line, use the
--quantity option. The quantity taken applies to the product in the
[root@server1 ~]# subscription-manager attach --pool=XYZ01234567 --quantity=2
One important thing in stacking is understanding how things are counted. There are two rules with counting subscriptions:
A socket pair requires a single subscription. (A single socket is still treated as a socket pair; likewise, an odd-number of sockets is treated as pairs.)
A virtual guest requires half a subscription.
The displayed quantities for subscriptions may be different than what is purchased because of the fact that a virtual guest is half of a subscription.
To make the subscription pool always come out in a whole number, the pool of available subscriptions is multiplied by two. If there are 15 Red Hat Enterprise Linux subscriptions purchased, than the displayed pool of available subscriptions is 30. This allows individual virtual machines to take a single subscription. This also means that it appears a physical system appears to use two subscriptions per socket pair.
Both the number of subscriptions total and the number of subscriptions consumed by both physical and virtual systems is fundamentally the same.