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The Role of Layer 4-7 Services in Scaling Applications for the Cloud-Computing Data Center

The Cloud Challenge
Cloud computing is increasing demands on applications and the application-delivery infrastructure must change to meet the challenge. Virtualization does not solve the problems with applications scaling, in fact it adds complexity. Infrastructure alone does not solve the challenge either. You don’t want to oversubscribe or just add capacity on demand. The infrastructure needs to respond to user demand based on business value and maintain a favorable cost structure. This means that you need intelligent load processing to manage scale, especially given the evolution of applications, which now make numerous backend function calls, which create more traffic than at the front end.

The Need for Scale
Cloud-computing applications are characterized by stateful access, with differentiated service levels, charged to the end user using the pay-per-use pricing model. Implicit in this model is the assumption that a cloud application is always on. Scaling the cloud delivery model to an Internet scale (millions of users) is a challenge that next-generation Layer 4–7 infrastructure needs to overcome.

Scaling a cloud application involves scaling three mechanisms: location (mobility), replication, and load balancing. Virtualization was an early catalyst for cloud computing because it substantially lowered the cost of replication and mobility of a prepackaged application. It does not, however, solve the load-balancing problem. Load balancing involves scaling the address, name space, transport, session, identity, and business logic of the application. Clustering enables scaling of application business logic but leaves the rest of the problem to a proxy infrastructure.
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