Elasticity as a service for federated cloud testbeds This paper presents the design, real-world deployment and evaluation of FOKUS Cloud Broker’s core component, the Elasticity Engine. The engine enables Elasticity as a Service, by providing dynamic and optimized cloud resource allocation for federated cloud platform environments. Deployed and evaluated within the European large-scale, multi-site cloud experimental facility BonFIRE this work provides a realistic assertion of the performance of the Elasticity Engine’s cloud resource allocation performance. Being a very typical scenario for today’s cloud platform users who are having the free choice to select amongst multiple cloud platform offerings, this work provides a rough, but realistic assertion on what can be expected of an elastic multi-cloud resource provisioning system in terms of performance.