Enterprises deploy their middlebox services in cloud seeking for easy management, flexible scalability and economic savings. However, existing elastic virtual network function(VNF) placement strategy often leads to an unpredictable placing location due to the ever-changing workload, which may waste much precious bandwidth resource and bring a lot of VM operation overhead(e.g. VM launch, termination and migration). A key problem for cloud providers is how to conduct an effective service placement and provide resource provision according to various workload, satisfying the bandwidth requirement of each service while saving as much cloud resource as possible. In this paper we solve both the virtual network function(VNF) placement and scaling problem based on preplanned allocation with bandwidth guarantee. We first propose a concept of VNF instance communication graph to describe the bandwidth demand of each VNF instance and explore the placement requirement for bandwidth savings. Then we design an on-line heuristic algorithm to achieve approximate optimal allocation. At last, we also provide an off-line optimal solution for comparison. Our simulation shows that our heuristic solution saves 20% more bandwidth resource and reduce more VM migration overhead than existing elastic placement solution. Its performance is also very close to the optimal solution.
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