1. A system for supporting a dynamic resource broker in a transactional middleware machine environment, comprising: one or more microprocessors; a deployment center running on the one or more microprocessors in the transactional middleware machine environment; and one or more deployment agents, each of which is associate with a transactional middleware machine of a plurality of transactional middleware machines in a transactional domain in the transactional middleware machine environment, wherein the deployment center operates to receive machine usage information from the one or more deployment agents, and wherein the deployment center operates to dynamically scale up/down resources used in the transactional domain based on the resource usage information collected by the one or more deployment agents.