In order to reduce operational expenditure (OPEX), network function virtualization infrastructure (NFVI) should be distributed over multiple geographical locations and managed by a centralized and unified management and orchestration system (MANO). In addition, the NFV platform is required to archive a high level of availability and scalability for virtual network functions (VNFs) across multi-site clouds. In this paper, we introduce clustering service architecture to provide available and scalable VNFs over multi-site cloud infrastructures. In particular, we introduce a new policy template in order to support multi-site deployment and policy-based management for VNF clusters in multisite environment. By implementing our proposal using open source Openstack Tacker project, we show the feasibility of our proposal.