As the cloud market is growing fast and more and more enterprises are moving their services to the cloud, assurance of cloud service quality becomes one of the key success factors of cloud business. Due to the dynamic nature of the cloud, it's more complicated to manage and guarantee quality level in the cloud than that in the telecommunication. In order to address these issues, we developed a service assurance oriented platform, Cloud BOSS, which has the capabilities of monitoring and measuring, problem management, and quality management. Every module in this platform cooperates with each other via standard JMX (Java Management Extensions) interfaces. An end-to-end SLA (Service Level Agreement) mechanism was also depicted to show how we manage to meet the service agreements with customers and demonstrate a practical way of mapping KPIs (Key Performance Indicators) to KQIs (Key Quality Indicators).