Just as liquids adapt their shape to the one of their container, liquid architectures feature a high degree of adaptability so that they can provide scalability to applications as they are executed on a wide variety of heterogeneous deployment environments. In this paper we enumerate the properties to be guaranteed by so-called liquid service-oriented architectures and define a set of design constraints that make up a novel architectural style for liquid architectures. These constraints drive the careful construction of a pattern, the Restful Actor (Reactor), which enables to deliver the required scalability by means of replication of its constituent parts. Reactors feature a Restful Web service interface and a composable architecture which is capable of delivering scalability and high performance in a way that is independent from the chosen deployment infrastructure. We discuss how the Reactor can be deployed to run on distributed (shared-nothing) execution environments typical of virtualized Cloud computing environments as well as on modern multicore processors with shared memory architectures.