I believe a Cloud-enabled-Application should have the following characteristic in its fundamental design.
Traditional SaaS App typically run within a single data center and assume low latency among server components. Now in the cloud environment that span many distant geographic locations, but the assumption of low latency cannot hold any more. We need to be “smarter” when choosing where to deploy to avoid the situation of putting frequently communicating components between far-distant locations. “Cloud-enabled SaaS app” need to be aware of latency difference and built in self-configuring and self-tuning mechanism to cope with that.
Traditional SaaS app typically run on already purposed hardware where utilization efficiency is not a concern. Now with the “pay as you go” model, application need to pay more attention to its usage pattern and efficiency of underlying resources because it will affect the operation cost. Cloud-enabled SaaS application need to understand the cost model of different resources utilization (such as CPU cost may be very different from Bandwidth cost) and adjust their usage strategy to minimize the operation cost.
Traditional SaaS app typically run on a fully trusted data center based on perimeter security. But in the Hybrid cloud model, the perimeter being drawn is very different now. Application need to carefully select where to store its data such that sensitivity will not be leaking. This involve careful determination of storage provider or use encryption for protection.
Capitalize on Elasticity
Traditional SaaS App is not used to large-scale growth / shrink of compute resources and typically haven’t designed well to handle how data get distributed to newly joined machines (in a growth scenario) or redistributed among remaining machines (in a shrink scenario). This ends up having a very inefficient use of network bandwidth and results in high cost and low performance. More sophisticated data distribution protocol that align with the growth and shrink dimension is needed for “Cloud-enabled SaaS app”