In recent years, cloud computing has become a significant technology trend because of various advantages including cost savings, flexibility, high availability, and scalability using virtualization technology. However, one of the concerns for using cloud computing is security. In fact, there are multiple attack surfaces in virtualized environments. In this paper, we build a fault tolerant cloud architecture using nested virtualization. With our constructed cloud architecture, we argue that a malicious virtual machine cannot subvert the whole virtual machines on the physical host machine. To support this, we compare the performance of two types of virtual machines (i.e., nested virtual machines and regular virtual machines). Results provide encouraging support for the validity of our cloud architecture with negligible performance degradation while having fault tolerance.