Also, we may not want multiple services to load balance. For example, we may have a volume agreement with the primary service provider that gives us substantial discounts if we meet certain usage quotas. Splitting the traffic across two providers will likely cost us more. Alternatively, we may be using a low-cost provider as our primary service provider and want to switch over to a premium provider only when the low-cost provider fails. (For an excellent discussion of architectural decisions driven by licensing considerations, see [Hohmann].)
