Resource sharing can gain economies of scale and increase utilization of cloud infrastructure, a critical challenge of which is how to design efficient resource sharing solutions among self-interested cloud providers. Cloud federation can realize resource sharing, but the existing methods of forming federation need complex computation to guarantee the stability of federation. To address this shortcoming, after analyzing an optimal allocation approach of service requests among clouds, we propose a pareto optimal resource sharing solution named Cloud Light-Federation Sharing (CLFS), in which each cloud can choose its own optimal strategies individually and federation can be formed without complex computation for allocation of service requests and profits. In addition, an optimal resource sharing solution named Cloud Cooperative-Federation Sharing (CCFS) was also designed, in which cloud providers are fully cooperative and have fair profit allocation. The experimental results show that the two federation methods can significantly improve the total utility and decrease the number of dropped jobs. Although the federation rules of Cloud Light-Federation Sharing are simple, its performance is still very close to that of Cloud Cooperative-Federation Sharing.