A policy that specifies the conditions for resource
expiration (i.e., automatic resource deletion).
Specifies the "time-to-live" duration for an associated
resource. The resource expires if it is not active for a
period of ttl. The definition of "activity" depends on
the type of the associated resource. The minimum and maximum
allowed values for ttl depend on the type of the
associated resource, as well. If ttl is not set, the
associated resource never expires.