Web 2.0 applications as social networking websites deal with a dynamic and various transaction workload. A middleware approach can be considered as a suitable solution for facing those various workloads. However, even if the middleware resources may be distributed for scalability and availability, they can be a bottleneck or underused when the workload varies permanently. We propose a solution that allows to add and remove dynamically resources of a distributed middleware. The proposed solution permits to handle transactions rapidly while using few middleware resources to reduce financial costs. Actually, we design an elasticity mechanism that distributes almost uniformly the transaction workload among the existing resources and adjusts the optimal number of nodes according to the workload variation. A simulation with cloudSim shows the effectiveness of our solution and its benefits.