7. vCloud Service Control : 7.1 vCloud Service Governance and Lifecycle Management : 7.1.2 Service Level Management : 7.1.2.3. Example
   
7.1.2.3. Example
The following is a use case example for an organization with an IaaS layer hosted by a public vCloud provider, but PaaS and SaaS layers are maintained internally.
Figure 10. Example Organization with Public vCloud IaaS and Private vCloud PaaS/SaaS Layers
The SLAs shown are for illustration purposes only and are a subset of the total number of SLAs created within an organization in such a case.
SLAs in this example are:
*IaaS Layer:
*Uptime/Availability SLA signed with the external vCloud service provider.
*Network performance SLA signed with the external service provider.
*Request Fulfillment SLA – Measure of response time for provisioning and access configuration requests.
*Restore time SLA.
*PaaS Layer:
*Uptime/Availability SLA for development environment.
*Uptime/Availability SLA for critical development environment components.
*Restore time SLA for development environment.
*SaaS Layer:
*Uptime/Availability SLA specific to an application.
*Application response time SLA – Measure of how the application is performing for the business users.
*Time to resolution SLA – Time to recover an application in case of a failure.
Given this example, the following are some key conclusions:
*SLAs, OLAs and KPIs are relevant at all levels within a vCloud stack. These agreements are required to provide efficiency and accountability at every layer, for both external providers and internal IT groups.
*These SLAs, OLAs and KPIs need to be managed within every layer to help isolate systemic problems and eliminate delays.
*SLAs can be between external vendors or providers of vCloud services, or between internal IT groups. An organization can choose whether to implement a private, public, or hybrid vCloud. At every layer, SLAs give organizations this flexibility by guaranteeing availability and quality of service.
*There are interrelationships between SLAs set up at different vCloud layers. A change in quality of service or breach of an SLA at a lower vCloud layer may impact multiple SLAs in a higher vCloud layer. In this example, if there is a breach of a performance SLA that results in the external vCloud provider’s inability to support OS performance needs, this breach has a ripple effect at the SaaS layer, decreasing application performance and response time for business users.
*SLAs need to be continuously managed and evaluated to maintain quality of service in a vCloud. Business needs are continuously evolving, resulting in changing vCloud business requirements. SLAs must be continuously updated to reflect current business requirements.
Consider the impact of adding another 1000 users to a particular application. Given this new demand the application criticality is increased and the application is classified as mission critical. This business change means that SLAs supporting the application may need to be updated to provide increased uptime and availability. This may lead to increased demands at the IaaS layer, so SLAs with the external IaaS provider may have to be expanded.