© Proceedings of the 2nd International Workshop on Hot Topics in Autonomic Computing, HotAC 2007, Held in conjunction with ICAC 2007. All rights reserved. This paper introduces Automat, a testbed architecture and prototype for research in autonomic services and hosting centers. Automat is an interactive web-based laboratory in which users allocate resources from an ondemand server cluster to experiment with controller policies for sense-and-respondmonitoring and adaptation by hosted services and, crucially, by the hosting center itself. Users may explore the interactions of components selected from a menu of applications, workloads, faultloads, and controllers, or install their own components. Components may include view extensions as plugins to a Web portal interface, enabling users to monitor and interact with controllers during an experiment.