5. Creating and Managing vApps : 5.6 Establishing Service Levels : 5.6.2 vCloud Layers and Service Level Agreements
   
5.6.2 vCloud Layers and Service Level Agreements
A typical vCloud-computing environment consists of multiple layers, such as IaaS, Platform as a Service (PaaS), and Software as a Service (SaaS). Consumers, based on their business requirements, have a number of options for implementing the vCloud stack, including:
*Creating a private vCloud.
*Using a public vCloud provider.
*Adopting a hybrid vCloud model in which both private and public vCloud resources are used.
The ability of an organization to guarantee availability and performance at every vCloud layer enables this flexibility. Flexibility is achieved by establishing SLAs externally with service providers or by creating SLAs internally for a private vCloud.
For an organization with an IaaS layer that is hosted by a public vCloud provider but where PaaS and SaaS layers are maintained internally, the following SLAs might apply:
*IaaS layer:
*Uptime and Availability SLA – Established with the external vCloud service provider.
*Network Performance SLA – Established with the external vCloud service provider.
*Request Fulfillment SLA – Measure of response time for provisioning and access configuration requests.
*Restore Time SLA.
*PaaS layer:
*Uptime and Availability SLA – For development environment.
*Uptime and Availability SLA – For critical development environment components.
*Restore Time SLA – For development environment.
*SaaS layer:
*Uptime and Availability SLA – Specific to an application.
*Application Response Time SLA – Measure of how the application performs for the business users.
*Time to Resolution SLA – Time to recover an application in case of failure.