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WSO2 Private PaaS uses two smart policies: Auto-scaling policy and Deployment policy. Auto-scaling parameters, which are defined via the auto-scaling policy related parameters and the deployment policy related parameters, are used to calibrate the elasticity of the system. The auto-scaling policies and deployment policies need to be defined and deployed before users subscribe to a cartridge. In single tenant cartridges the auto-scaling policy and deployment policy that needs to be used for the subscription needs to be selected at the time of subscription. However, in multi-tenant cartridges the auto-scaling policy and deployment policy to be used needs to be defined when deploying the multi-tenant service cluster. 

The auto-scaling and deployment policies can be used to derive a cloud SLA from the platform as a service (PaaS) layer, which in turn will benefit the software as a service (SaaS) layer applications. For example, if you want to derive five-9’s availability ( 9999.999% 999%) , then you have to maintain a minimum instances count and run on different cloud vendors, different regions, different zones etc. The latter requirement can be fulfilled if defined in the deployment policies.